From d740141462ccd70a75f15f4068189ce88e76f35b Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:00:12 +1100
Subject: [PATCH 01/16] fix(export): recognise video players by type, not class
 name

---
 src/core/export/video-frame-processor.ts |  9 +++-----
 tests/export-coordinator.test.ts         |  7 +++++-
 tests/export-preflight.test.ts           | 10 ++++++--
 tests/export-video-frames.test.ts        | 29 ++++++++++++++++++++++++
 4 files changed, 46 insertions(+), 9 deletions(-)
 create mode 100644 tests/export-video-frames.test.ts

diff --git a/src/core/export/video-frame-processor.ts b/src/core/export/video-frame-processor.ts
index ec196917..af4d1670 100644
--- a/src/core/export/video-frame-processor.ts
+++ b/src/core/export/video-frame-processor.ts
@@ -1,3 +1,4 @@
+import { PlayerType } from "@canvas/players/player";
 import { Input, UrlSource, MP4, WEBM, CanvasSink, type InputVideoTrack } from "mediabunny";
 import * as pixi from "pixi.js";
 
@@ -15,13 +16,9 @@ export interface VideoPlayerExtended {
 	getLength?(): number;
 }
 
+// By type, not class name: minification renames classes, and a luma matte can hold a video texture too.
 export function isVideoPlayer(player: unknown): player is VideoPlayerExtended {
-	if (!player || typeof player !== "object") return false;
-	const p = player as Record<string, unknown>;
-	const name = p.constructor?.name;
-	if (name === "RichTextPlayer" || name === "RichCaptionPlayer") return false;
-	const texture = p["texture"] as { source?: { resource?: unknown } } | undefined;
-	return name === "VideoPlayer" || texture?.source?.resource instanceof HTMLVideoElement;
+	return typeof player === "object" && player !== null && "playerType" in player && player.playerType === PlayerType.Video;
 }
 
 interface ClipDecoder {
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index 796b77ad..88c29b50 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -44,7 +44,10 @@ jest.mock("mediabunny", () => ({
 	WEBM: {}
 }));
 
+// Player modules extend pixi filters at load.
 jest.mock("pixi.js", () => ({
+	// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports -- jest.mock factories can't use imports
+	...require("./helpers/pixi-mock-filters").pixiFilterStubs,
 	Rectangle: jest.fn().mockImplementation((x: number, y: number, width: number, height: number) => ({ x, y, width, height })),
 	Texture: { from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
 }));
@@ -337,8 +340,10 @@ describe("off-screen export", () => {
 describe("speed", () => {
 	it("decodes each video frame at the player's own source time for that frame", async () => {
 		const { exporter, edit } = createHarness();
-		// isVideoPlayer recognises a player by its class name; getSourceTime stands in for the preview's speed mapping.
+		// getSourceTime stands in for the preview's speed mapping.
 		class VideoPlayer {
+			playerType = "video";
+
 			clipId = "fast-clip";
 
 			needsResolution = false;
diff --git a/tests/export-preflight.test.ts b/tests/export-preflight.test.ts
index 167bf236..e3f3ad59 100644
--- a/tests/export-preflight.test.ts
+++ b/tests/export-preflight.test.ts
@@ -16,7 +16,12 @@ jest.mock("mediabunny", () => ({
 	WEBM: {}
 }));
 
-jest.mock("pixi.js", () => ({ Texture: { from: jest.fn() } }));
+// Player modules extend pixi filters at load.
+jest.mock("pixi.js", () => ({
+	// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports -- jest.mock factories can't use imports
+	...require("./helpers/pixi-mock-filters").pixiFilterStubs,
+	Texture: { from: jest.fn() }
+}));
 
 const customFonts: Record<string, string> = {
 	"Brand Sans|400": "https://example.com/brand-sans.ttf",
@@ -140,8 +145,9 @@ describe("findBrowserIssue", () => {
 
 describe("VideoFrameProcessor.initialize", () => {
 	it("reports a video the browser can't decode as video-source", async () => {
-		// isVideoPlayer recognises a player by its class name.
 		class VideoPlayer {
+			playerType = "video";
+
 			clipId = "mov-clip";
 
 			clipConfiguration = { asset: { type: "video", src: "https://example.com/clip.mov" } };
diff --git a/tests/export-video-frames.test.ts b/tests/export-video-frames.test.ts
new file mode 100644
index 00000000..48bb429f
--- /dev/null
+++ b/tests/export-video-frames.test.ts
@@ -0,0 +1,29 @@
+/** @jest-environment jsdom */
+
+import { isVideoPlayer } from "@core/export/video-frame-processor";
+
+jest.mock("mediabunny", () => ({ Input: jest.fn(), UrlSource: jest.fn(), CanvasSink: jest.fn(), MP4: {}, WEBM: {} }));
+
+// Player modules extend pixi filters at load; the frame processor only builds textures.
+jest.mock("pixi.js", () => ({
+	// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports -- jest.mock factories can't use imports
+	...require("./helpers/pixi-mock-filters").pixiFilterStubs,
+	Texture: { from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
+}));
+
+describe("isVideoPlayer", () => {
+	it("recognises a video player by its type, whatever name the bundler gives its class", () => {
+		// The published build renames VideoPlayer to something like this.
+		class UK {
+			playerType = "video";
+		}
+
+		expect(isVideoPlayer(new UK())).toBe(true);
+	});
+
+	it("leaves out a luma matte drawn from a video", () => {
+		const luma = { playerType: "luma", texture: { source: { resource: document.createElement("video") } } };
+
+		expect(isVideoPlayer(luma)).toBe(false);
+	});
+});

From 36d992e5f02cd5bff6bee688d09af8a6a81e426a Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:01:02 +1100
Subject: [PATCH 02/16] fix(export): release inputs without a video track and
 unfreeze every paused video

---
 src/core/export/video-frame-processor.ts | 16 ++++++++----
 tests/export-video-frames.test.ts        | 33 +++++++++++++++++++++++-
 2 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/src/core/export/video-frame-processor.ts b/src/core/export/video-frame-processor.ts
index af4d1670..cf7e232f 100644
--- a/src/core/export/video-frame-processor.ts
+++ b/src/core/export/video-frame-processor.ts
@@ -36,10 +36,11 @@ interface ClipDecoder {
  */
 export class VideoFrameProcessor {
 	private decoders = new Map<VideoPlayerExtended, ClipDecoder>();
+	private paused = new Set<VideoPlayerExtended>();
 
 	/** Open a decoder per video clip; a source the browser can't decode comes back as an issue. */
 	async initialize(clips: ReadonlyArray<unknown>): Promise<ExportIssue[]> {
-		const players = clips.filter(isVideoPlayer) as VideoPlayerExtended[];
+		const players = clips.filter(isVideoPlayer);
 		const issues: ExportIssue[] = [];
 
 		await Promise.all(
@@ -47,6 +48,7 @@ export class VideoFrameProcessor {
 				const src = this.getVideoKey(player);
 				if (!src) return;
 				const input = new Input({ source: new UrlSource(src), formats: [MP4, WEBM] });
+				let kept = false;
 				try {
 					const track = await input.getPrimaryVideoTrack();
 					if (!track) return;
@@ -57,10 +59,12 @@ export class VideoFrameProcessor {
 						sink: new CanvasSink(track, { poolSize: 2 }),
 						originalTexture: player.texture
 					});
+					kept = true;
 				} catch (error) {
-					input.dispose();
 					console.warn("Export: can't decode video", src, error);
 					issues.push({ code: "video-source", message: "This video's format can't be decoded in the browser.", clipId: player.clipId ?? undefined });
+				} finally {
+					if (!kept) input.dispose();
 				}
 			})
 		);
@@ -99,13 +103,14 @@ export class VideoFrameProcessor {
 
 	/** Pause the live <video> elements and return the export's video players. */
 	disableVideoPlayback(clips: ReadonlyArray<unknown>): VideoPlayerExtended[] {
-		const players = clips.filter(isVideoPlayer) as VideoPlayerExtended[];
+		const players = clips.filter(isVideoPlayer);
 		for (const player of players) {
 			const resource = player.texture?.source?.resource;
 			if (resource instanceof HTMLVideoElement) resource.pause();
 			// The decoder drives frames during export; stop the player's own video update.
 			// eslint-disable-next-line no-param-reassign
 			player.skipVideoUpdate = true;
+			this.paused.add(player);
 		}
 		return players;
 	}
@@ -123,11 +128,12 @@ export class VideoFrameProcessor {
 				}
 				decoder.texture?.destroy(true);
 			}
-			// eslint-disable-next-line no-param-reassign
-			player.skipVideoUpdate = false;
 			decoder.input.dispose();
 		}
 		this.decoders.clear();
+		// Every player the export paused, decoded or not; one left skipping updates stays frozen in the editor.
+		for (const player of this.paused) player.skipVideoUpdate = false;
+		this.paused.clear();
 	}
 
 	getVideoKey(player: VideoPlayerExtended): string {
diff --git a/tests/export-video-frames.test.ts b/tests/export-video-frames.test.ts
index 48bb429f..610dfc50 100644
--- a/tests/export-video-frames.test.ts
+++ b/tests/export-video-frames.test.ts
@@ -1,6 +1,7 @@
 /** @jest-environment jsdom */
 
-import { isVideoPlayer } from "@core/export/video-frame-processor";
+import { isVideoPlayer, VideoFrameProcessor } from "@core/export/video-frame-processor";
+import { Input } from "mediabunny";
 
 jest.mock("mediabunny", () => ({ Input: jest.fn(), UrlSource: jest.fn(), CanvasSink: jest.fn(), MP4: {}, WEBM: {} }));
 
@@ -27,3 +28,33 @@ describe("isVideoPlayer", () => {
 		expect(isVideoPlayer(luma)).toBe(false);
 	});
 });
+
+describe("VideoFrameProcessor", () => {
+	const videoPlayer = (src = "https://example.com/clip.mp4") => ({
+		playerType: "video",
+		clipId: "clip-1",
+		clipConfiguration: { asset: { type: "video", src } },
+		skipVideoUpdate: false,
+		getSourceTime: () => 0
+	});
+
+	it("releases the input of a source with no video track", async () => {
+		const dispose = jest.fn();
+		jest.mocked(Input).mockImplementationOnce(() => ({ getPrimaryVideoTrack: async () => null, dispose }) as unknown as InstanceType<typeof Input>);
+
+		await new VideoFrameProcessor().initialize([videoPlayer()]);
+
+		expect(dispose).toHaveBeenCalledTimes(1);
+	});
+
+	it("restarts every paused video player, including one that got no decoder", () => {
+		const processor = new VideoFrameProcessor();
+		const player = videoPlayer("");
+
+		processor.disableVideoPlayback([player]);
+		expect(player.skipVideoUpdate).toBe(true);
+		processor.restore();
+
+		expect(player.skipVideoUpdate).toBe(false);
+	});
+});

From dee4f5a46c9174ec269990d320d42814ecc09158 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:02:37 +1100
Subject: [PATCH 03/16] fix(export): keep a video's crop in exported frames

---
 src/core/export/video-frame-processor.ts |  8 +++--
 tests/export-coordinator.test.ts         |  5 ++-
 tests/export-video-frames.test.ts        | 44 ++++++++++++++++++++++--
 3 files changed, 50 insertions(+), 7 deletions(-)

diff --git a/src/core/export/video-frame-processor.ts b/src/core/export/video-frame-processor.ts
index cf7e232f..c7c674dc 100644
--- a/src/core/export/video-frame-processor.ts
+++ b/src/core/export/video-frame-processor.ts
@@ -83,12 +83,14 @@ export class VideoFrameProcessor {
 		if (!wrapped) return;
 
 		if (!decoder.texture) {
+			const live = decoder.originalTexture;
 			const canvas = document.createElement("canvas");
-			canvas.width = wrapped.canvas.width;
-			canvas.height = wrapped.canvas.height;
+			// Sized like the live video texture, so its frame (the asset's crop) picks the same pixels here.
+			canvas.width = live?.source.width || wrapped.canvas.width;
+			canvas.height = live?.source.height || wrapped.canvas.height;
 			decoder.canvas = canvas;
 			decoder.ctx = canvas.getContext("2d", { alpha: true }) ?? undefined;
-			decoder.texture = pixi.Texture.from(canvas);
+			decoder.texture = new pixi.Texture({ source: pixi.Texture.from(canvas).source, frame: live?.frame });
 		}
 
 		decoder.ctx?.drawImage(wrapped.canvas, 0, 0, decoder.canvas!.width, decoder.canvas!.height);
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index 88c29b50..4a9b1705 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -49,7 +49,10 @@ jest.mock("pixi.js", () => ({
 	// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports -- jest.mock factories can't use imports
 	...require("./helpers/pixi-mock-filters").pixiFilterStubs,
 	Rectangle: jest.fn().mockImplementation((x: number, y: number, width: number, height: number) => ({ x, y, width, height })),
-	Texture: { from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
+	Texture: Object.assign(
+		jest.fn((options: object) => ({ ...options, destroy: jest.fn() })),
+		{ from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
+	)
 }));
 
 // The canvas package needs TextEncoder, which jsdom lacks; the export only uses its font-name parser.
diff --git a/tests/export-video-frames.test.ts b/tests/export-video-frames.test.ts
index 610dfc50..c88074f9 100644
--- a/tests/export-video-frames.test.ts
+++ b/tests/export-video-frames.test.ts
@@ -1,7 +1,7 @@
 /** @jest-environment jsdom */
 
-import { isVideoPlayer, VideoFrameProcessor } from "@core/export/video-frame-processor";
-import { Input } from "mediabunny";
+import { isVideoPlayer, VideoFrameProcessor, type VideoPlayerExtended } from "@core/export/video-frame-processor";
+import { CanvasSink, Input } from "mediabunny";
 
 jest.mock("mediabunny", () => ({ Input: jest.fn(), UrlSource: jest.fn(), CanvasSink: jest.fn(), MP4: {}, WEBM: {} }));
 
@@ -9,9 +9,17 @@ jest.mock("mediabunny", () => ({ Input: jest.fn(), UrlSource: jest.fn(), CanvasS
 jest.mock("pixi.js", () => ({
 	// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports -- jest.mock factories can't use imports
 	...require("./helpers/pixi-mock-filters").pixiFilterStubs,
-	Texture: { from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
+	Texture: Object.assign(
+		jest.fn((options: object) => ({ ...options, destroy: jest.fn() })),
+		{ from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
+	)
 }));
 
+beforeAll(() => {
+	// jsdom has no 2D canvas; the processor only draws into one.
+	Object.assign(HTMLCanvasElement.prototype, { getContext: () => ({ drawImage: jest.fn() }) });
+});
+
 describe("isVideoPlayer", () => {
 	it("recognises a video player by its type, whatever name the bundler gives its class", () => {
 		// The published build renames VideoPlayer to something like this.
@@ -58,3 +66,33 @@ describe("VideoFrameProcessor", () => {
 		expect(player.skipVideoUpdate).toBe(false);
 	});
 });
+
+describe("VideoFrameProcessor.replaceVideoTexture", () => {
+	it("keeps the crop the player's own texture applies", async () => {
+		const live = { source: { width: 1920, height: 1080 }, frame: { x: 192, y: 0, width: 1536, height: 1080 } };
+		const player = {
+			playerType: "video",
+			clipConfiguration: { asset: { type: "video", src: "https://example.com/clip.mp4" } },
+			texture: live,
+			getSourceTime: () => 0
+		};
+		jest
+			.mocked(Input)
+			.mockImplementationOnce(
+				() => ({ getPrimaryVideoTrack: async () => ({ canDecode: async () => true }), dispose: jest.fn() }) as unknown as InstanceType<typeof Input>
+			);
+		jest
+			.mocked(CanvasSink)
+			.mockImplementationOnce(
+				() => ({ getCanvas: async () => ({ canvas: { width: 1920, height: 1080 } }) }) as unknown as InstanceType<typeof CanvasSink>
+			);
+		const processor = new VideoFrameProcessor();
+		await processor.initialize([player]);
+
+		await processor.replaceVideoTexture(player as unknown as VideoPlayerExtended);
+
+		expect(player.texture).not.toBe(live);
+		expect(player.texture).toMatchObject({ frame: live.frame });
+		processor.restore();
+	});
+});

From d9775cb666bcc59d38cf3e120cddbb4dd0912082 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:03:17 +1100
Subject: [PATCH 04/16] fix(export): refuse luma mattes drawn from video

---
 readme.md                           |  1 +
 src/core/export/export-preflight.ts |  4 +++-
 src/core/export/export-utils.ts     | 13 ++++++++++++-
 tests/export-preflight.test.ts      |  9 +++++++++
 4 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/readme.md b/readme.md
index 7edbd035..7e269655 100644
--- a/readme.md
+++ b/readme.md
@@ -367,6 +367,7 @@ Before encoding, both methods check that the browser can draw the edit the way a
 | `effect` | An effect without a preset in the editor |
 | `transition` | A transition without a preset in the editor |
 | `font` | A font that is neither built in nor listed in `timeline.fonts` |
+| `luma` | A luma matte whose source is a video |
 | `too-long` | The edit runs longer than five minutes |
 | `browser` | The browser can't encode H.264 at the output size |
 
diff --git a/src/core/export/export-preflight.ts b/src/core/export/export-preflight.ts
index 45e11fef..c5ab30ce 100644
--- a/src/core/export/export-preflight.ts
+++ b/src/core/export/export-preflight.ts
@@ -4,7 +4,7 @@ import type { Edit } from "@core/edit-session";
 import { resolveFontPath } from "@core/fonts/font-config";
 import { NAMED_FONT_WEIGHTS } from "@core/fonts/font-weights";
 import { isPendingAiAsset } from "@core/shared/ai-asset-utils";
-import { isTextHtml } from "@core/shared/asset-utils";
+import { inferAssetTypeFromUrl, isTextHtml } from "@core/shared/asset-utils";
 import type { ResolvedClip } from "@schemas";
 import { canEncodeVideo } from "mediabunny";
 
@@ -39,6 +39,8 @@ function findClipIssues(edit: PreflightEdit, clip: ResolvedClip): ExportIssue[]
 	if (asset.type === "video" && asset.chromaKey) add("chroma-key", "Chroma key isn't available in the browser.");
 	if (clip.filter && clip.filter !== "none") add("filter", `The ${clip.filter} filter isn't available in the browser.`);
 	if (asset.type === "html5" || (asset.type === "html" && !isTextHtml(asset.html))) add("html", "This HTML clip can only be rendered in the cloud.");
+	// Mattes redraw in the editor's update loop, which export doesn't run, so a video matte would hold one frame.
+	if (asset.type === "luma" && inferAssetTypeFromUrl(asset.src) === "video") add("luma", "Video luma mattes aren't available in the browser.");
 	if (clip.effect && !animates(new EffectPresetBuilder(clip).buildRelative(UNIT_SIZE, UNIT_SIZE))) {
 		add("effect", `The ${clip.effect} effect isn't available in the browser.`);
 	}
diff --git a/src/core/export/export-utils.ts b/src/core/export/export-utils.ts
index 74b934d1..8b499dac 100644
--- a/src/core/export/export-utils.ts
+++ b/src/core/export/export-utils.ts
@@ -35,7 +35,18 @@ export class SimpleLRUCache<T> extends Map<string, T> {
 }
 
 export type ExportIssueCode =
-	"ai-pending" | "output-format" | "video-source" | "chroma-key" | "filter" | "html" | "effect" | "transition" | "font" | "too-long" | "browser";
+	| "ai-pending"
+	| "output-format"
+	| "video-source"
+	| "chroma-key"
+	| "filter"
+	| "html"
+	| "effect"
+	| "transition"
+	| "font"
+	| "luma"
+	| "too-long"
+	| "browser";
 
 export interface ExportIssue {
 	code: ExportIssueCode;
diff --git a/tests/export-preflight.test.ts b/tests/export-preflight.test.ts
index e3f3ad59..0ab5a201 100644
--- a/tests/export-preflight.test.ts
+++ b/tests/export-preflight.test.ts
@@ -119,6 +119,15 @@ describe("findEditIssues", () => {
 		expect(codes(withWeight("normal"))).toEqual(["font"]);
 	});
 
+	it("reports a luma matte drawn from a video as luma, and passes an image matte", () => {
+		expect(
+			codes([
+				clip({ id: "video-matte", asset: { type: "luma", src: "https://example.com/wipe.mp4?v=2" } }),
+				clip({ id: "image-matte", asset: { type: "luma", src: "https://example.com/wipe.png" } })
+			])
+		).toEqual(["luma"]);
+	});
+
 	it("reports an edit longer than the limit as too-long", () => {
 		expect(codes([], { duration: MAX_EXPORT_SECONDS + 1 })).toEqual(["too-long"]);
 		expect(codes([], { duration: MAX_EXPORT_SECONDS })).toEqual([]);

From 73694efa68ab8e8119120a93aa2b62861b29a1f8 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:04:17 +1100
Subject: [PATCH 05/16] fix(export): budget export length by encoded size as
 well as duration

---
 readme.md                             |  2 +-
 src/core/export/export-coordinator.ts |  2 +-
 src/core/export/export-preflight.ts   | 15 ++++++++++-----
 tests/export-preflight.test.ts        | 19 +++++++++++++++----
 4 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/readme.md b/readme.md
index 7e269655..f736376a 100644
--- a/readme.md
+++ b/readme.md
@@ -368,7 +368,7 @@ Before encoding, both methods check that the browser can draw the edit the way a
 | `transition` | A transition without a preset in the editor |
 | `font` | A font that is neither built in nor listed in `timeline.fonts` |
 | `luma` | A luma matte whose source is a video |
-| `too-long` | The edit runs longer than five minutes |
+| `too-long` | The edit runs longer than five minutes, or less above 1080p (75 seconds at 4K) |
 | `browser` | The browser can't encode H.264 at the output size |
 
 ## Merge Fields
diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index 8e1a2e57..6b140f4e 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -164,7 +164,7 @@ export class ExportCoordinator {
 	private async checkExportable(cfg: ExportConfig, signal?: AbortSignal): Promise<void> {
 		await waitForLoads(this.edit, signal);
 
-		const issues = findEditIssues(this.edit);
+		const issues = findEditIssues(this.edit, cfg.bitrate);
 		const browserIssue = await findBrowserIssue(cfg.size, cfg.bitrate);
 		if (browserIssue) issues.push(browserIssue);
 		issues.push(...(await this.videoProcessor.initialize(this.edit.getTracks().flat())));
diff --git a/src/core/export/export-preflight.ts b/src/core/export/export-preflight.ts
index c5ab30ce..72de70b0 100644
--- a/src/core/export/export-preflight.ts
+++ b/src/core/export/export-preflight.ts
@@ -8,10 +8,12 @@ import { inferAssetTypeFromUrl, isTextHtml } from "@core/shared/asset-utils";
 import type { ResolvedClip } from "@schemas";
 import { canEncodeVideo } from "mediabunny";
 
-import type { ExportIssue, ExportIssueCode } from "./export-utils";
+import { exportBitrate, type ExportIssue, type ExportIssueCode } from "./export-utils";
 
-/** The encoded file and the audio mix are both held in memory until the export finishes. */
+/** The audio mix is held in memory until the export finishes, and it grows with length at any size. */
 export const MAX_EXPORT_SECONDS = 300;
+/** The encoded video is held in memory too: five minutes' worth at 1080p, so larger outputs get less time. */
+export const MAX_EXPORT_BITS = MAX_EXPORT_SECONDS * exportBitrate({ width: 1920, height: 1080 });
 
 type PreflightEdit = Pick<Edit, "getResolvedEdit" | "getOutputFormat" | "getFontUrlByFamilyAndWeight" | "totalDuration">;
 
@@ -62,12 +64,15 @@ function findClipIssues(edit: PreflightEdit, clip: ResolvedClip): ExportIssue[]
 	return issues;
 }
 
-export function findEditIssues(edit: PreflightEdit): ExportIssue[] {
+export function findEditIssues(edit: PreflightEdit, bitrate: number): ExportIssue[] {
 	const issues: ExportIssue[] = [];
 	const format = edit.getOutputFormat();
 	if (format !== "mp4") issues.push({ code: "output-format", message: `The browser exports MP4 only, and this edit asks for ${format}.` });
-	if (edit.totalDuration > MAX_EXPORT_SECONDS) {
-		issues.push({ code: "too-long", message: `The browser exports up to ${MAX_EXPORT_SECONDS / 60} minutes of video.` });
+	if (edit.totalDuration > MAX_EXPORT_SECONDS || edit.totalDuration * bitrate > MAX_EXPORT_BITS) {
+		issues.push({
+			code: "too-long",
+			message: `The browser exports up to ${MAX_EXPORT_SECONDS / 60} minutes of video at 1080p, and less at larger sizes.`
+		});
 	}
 	for (const track of edit.getResolvedEdit().timeline.tracks) {
 		for (const clip of track.clips) issues.push(...findClipIssues(edit, clip));
diff --git a/tests/export-preflight.test.ts b/tests/export-preflight.test.ts
index 0ab5a201..e3a12a0c 100644
--- a/tests/export-preflight.test.ts
+++ b/tests/export-preflight.test.ts
@@ -1,4 +1,5 @@
 import { findBrowserIssue, findEditIssues, MAX_EXPORT_SECONDS } from "@core/export/export-preflight";
+import { exportBitrate } from "@core/export/export-utils";
 import { VideoFrameProcessor } from "@core/export/video-frame-processor";
 import { sec } from "@core/timing/types";
 import type { ResolvedClip } from "@schemas";
@@ -47,8 +48,10 @@ function editWith(
 	};
 }
 
-const codes = (clips: ResolvedClip[], options?: { format?: string; duration?: number }): string[] =>
-	findEditIssues(editWith(clips, options)).map(issue => issue.code);
+const HD_BITRATE = exportBitrate({ width: 1920, height: 1080 });
+
+const codes = (clips: ResolvedClip[], options?: { format?: string; duration?: number; bitrate?: number }): string[] =>
+	findEditIssues(editWith(clips, options), options?.bitrate ?? HD_BITRATE).map(issue => issue.code);
 
 describe("findEditIssues", () => {
 	it("passes an edit the browser draws the way the cloud does", () => {
@@ -59,11 +62,11 @@ describe("findEditIssues", () => {
 			clip({ asset: { type: "html", html: '<p data-html-type="text">Hi</p>' }, filter: "none" })
 		];
 
-		expect(findEditIssues(editWith(faithful))).toEqual([]);
+		expect(findEditIssues(editWith(faithful), HD_BITRATE)).toEqual([]);
 	});
 
 	it("reports a prompt clip that hasn't been generated as ai-pending", () => {
-		expect(findEditIssues(editWith([clip({ id: "prompt-clip", asset: { type: "image", prompt: "A red kite" } })]))).toEqual([
+		expect(findEditIssues(editWith([clip({ id: "prompt-clip", asset: { type: "image", prompt: "A red kite" } })]), HD_BITRATE)).toEqual([
 			{ code: "ai-pending", message: "This clip hasn't been generated yet.", clipId: "prompt-clip" }
 		]);
 	});
@@ -132,6 +135,14 @@ describe("findEditIssues", () => {
 		expect(codes([], { duration: MAX_EXPORT_SECONDS + 1 })).toEqual(["too-long"]);
 		expect(codes([], { duration: MAX_EXPORT_SECONDS })).toEqual([]);
 	});
+
+	it("gives larger outputs less time, since the encoded file is held in memory", () => {
+		const uhd = exportBitrate({ width: 3840, height: 2160 });
+
+		expect(codes([], { duration: MAX_EXPORT_SECONDS, bitrate: uhd })).toEqual(["too-long"]);
+		expect(codes([], { duration: MAX_EXPORT_SECONDS / 4, bitrate: uhd })).toEqual([]);
+		expect(codes([], { duration: MAX_EXPORT_SECONDS, bitrate: HD_BITRATE })).toEqual([]);
+	});
 });
 
 describe("findBrowserIssue", () => {

From 604fc30a532681989472c189e9fbd439a2ac0984 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:05:35 +1100
Subject: [PATCH 06/16] fix(export): honour a muted output and refuse range and
 scaleTo

---
 readme.md                             |  2 +-
 src/core/export/export-coordinator.ts |  3 ++-
 src/core/export/export-preflight.ts   |  5 +++++
 tests/export-coordinator.test.ts      | 25 +++++++++++++++++++++----
 tests/export-preflight.test.ts        | 18 +++++++++++-------
 5 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/readme.md b/readme.md
index f736376a..65a9077b 100644
--- a/readme.md
+++ b/readme.md
@@ -359,7 +359,7 @@ Before encoding, both methods check that the browser can draw the edit the way a
 | Code | Reason |
 | --- | --- |
 | `ai-pending` | A prompt clip hasn't been generated yet |
-| `output-format` | `output.format` isn't `mp4` |
+| `output-format` | `output.format` isn't `mp4`, or the edit sets `output.range` or `output.scaleTo` |
 | `video-source` | The browser can't decode a video (MP4 and WebM only) |
 | `chroma-key` | A video uses chroma key |
 | `filter` | A clip uses a filter |
diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index 6b140f4e..cb91608d 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -123,7 +123,8 @@ export class ExportCoordinator {
 			output.addVideoTrack(videoSource);
 
 			report(0.15, "Mixing audio...");
-			const mixedAudio = await this.audioProcessor.renderMix(this.edit.getTracks(), this.edit.totalDuration);
+			const muted = this.edit.getEdit().output?.mute === true;
+			const mixedAudio = muted ? null : await this.audioProcessor.renderMix(this.edit.getTracks(), this.edit.totalDuration);
 			throwIfAborted();
 			let audioSource: AudioBufferSource | null = null;
 			if (mixedAudio) {
diff --git a/src/core/export/export-preflight.ts b/src/core/export/export-preflight.ts
index 72de70b0..b981238d 100644
--- a/src/core/export/export-preflight.ts
+++ b/src/core/export/export-preflight.ts
@@ -68,6 +68,11 @@ export function findEditIssues(edit: PreflightEdit, bitrate: number): ExportIssu
 	const issues: ExportIssue[] = [];
 	const format = edit.getOutputFormat();
 	if (format !== "mp4") issues.push({ code: "output-format", message: `The browser exports MP4 only, and this edit asks for ${format}.` });
+	const { output } = edit.getResolvedEdit();
+	if (output.range) issues.push({ code: "output-format", message: "The browser exports the whole timeline, and this edit asks for a range." });
+	if (output.scaleTo) {
+		issues.push({ code: "output-format", message: `The browser exports at the edit's size, and this edit asks to scale to ${output.scaleTo}.` });
+	}
 	if (edit.totalDuration > MAX_EXPORT_SECONDS || edit.totalDuration * bitrate > MAX_EXPORT_BITS) {
 		issues.push({
 			code: "too-long",
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index 4a9b1705..fad8c6ba 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -8,7 +8,7 @@ import { ExportError, exportBitrate } from "@core/export/export-utils";
 import { calculateSizeFromPreset } from "@core/output-settings-manager";
 import { canEncodeVideo, CanvasSink, CanvasSource, Input, Output } from "mediabunny";
 
-const mockOutputs: Array<{ cancel: jest.Mock; state: string }> = [];
+const mockOutputs: Array<{ cancel: jest.Mock; addAudioTrack: jest.Mock; state: string }> = [];
 
 jest.mock("mediabunny", () => ({
 	Output: jest.fn().mockImplementation(({ target }: { target: { buffer: ArrayBuffer | null } }) => {
@@ -35,7 +35,7 @@ jest.mock("mediabunny", () => ({
 	Mp4OutputFormat: jest.fn(),
 	BufferTarget: jest.fn().mockImplementation(() => ({ buffer: null })),
 	CanvasSource: jest.fn().mockImplementation(() => ({ add: jest.fn().mockResolvedValue(undefined) })),
-	AudioBufferSource: jest.fn(),
+	AudioBufferSource: jest.fn().mockImplementation(() => ({ add: jest.fn().mockResolvedValue(undefined) })),
 	canEncodeVideo: jest.fn(),
 	Input: jest.fn(),
 	UrlSource: jest.fn(),
@@ -58,8 +58,10 @@ jest.mock("pixi.js", () => ({
 // The canvas package needs TextEncoder, which jsdom lacks; the export only uses its font-name parser.
 jest.mock("@shotstack/shotstack-canvas", () => ({ parseFontFamily: (family: string) => ({ family, weight: "400" }) }));
 
+const mockRenderMix = jest.fn();
+
 jest.mock("../src/core/export/audio-processor", () => ({
-	AudioProcessor: jest.fn().mockImplementation(() => ({ renderMix: jest.fn().mockResolvedValue(null) }))
+	AudioProcessor: jest.fn().mockImplementation(() => ({ renderMix: mockRenderMix }))
 }));
 
 const SIZE = { width: 4, height: 2 };
@@ -72,7 +74,7 @@ function createHarness() {
 		totalDuration: 1,
 		size: { ...SIZE },
 		tracks: [] as Array<Array<{ clipId: string; needsResolution: boolean }>>,
-		getEdit: () => ({ output: { fps: 2 } }),
+		getEdit: jest.fn(() => ({ output: { fps: 2 } as { fps: number; mute?: boolean } })),
 		getOutputFormat: jest.fn(() => "mp4"),
 		getResolvedEdit: () => ({ timeline: { tracks: [] }, output: { format: "mp4" } }),
 		getFontUrlByFamilyAndWeight: () => null,
@@ -115,6 +117,7 @@ beforeEach(() => {
 	document.body.innerHTML = "";
 	jest.mocked(canEncodeVideo).mockResolvedValue(true);
 	jest.mocked(CanvasSource).mockClear();
+	mockRenderMix.mockReset().mockResolvedValue(null);
 });
 
 describe("ExportCoordinator.exportBlob", () => {
@@ -298,6 +301,20 @@ describe("ExportCoordinator.exportBlob", () => {
 	});
 });
 
+describe("output settings", () => {
+	it("mixes no audio and adds no audio track for a muted output", async () => {
+		const { exporter, edit } = createHarness();
+		edit.getEdit.mockReturnValue({ output: { fps: 2, mute: true } });
+		mockRenderMix.mockResolvedValue({ duration: 1 });
+
+		await exporter.exportBlob();
+
+		expect(mockRenderMix).not.toHaveBeenCalled();
+		expect(mockOutputs[0].addAudioTrack).not.toHaveBeenCalled();
+		exporter.dispose();
+	});
+});
+
 describe("off-screen export", () => {
 	it("draws each frame from the viewport container at output size while the view stays where the user left it", async () => {
 		const { exporter, edit, renderer, viewport, viewAtExtract } = createHarness();
diff --git a/tests/export-preflight.test.ts b/tests/export-preflight.test.ts
index e3a12a0c..8e1690da 100644
--- a/tests/export-preflight.test.ts
+++ b/tests/export-preflight.test.ts
@@ -2,7 +2,7 @@ import { findBrowserIssue, findEditIssues, MAX_EXPORT_SECONDS } from "@core/expo
 import { exportBitrate } from "@core/export/export-utils";
 import { VideoFrameProcessor } from "@core/export/video-frame-processor";
 import { sec } from "@core/timing/types";
-import type { ResolvedClip } from "@schemas";
+import type { ResolvedClip, ResolvedEdit } from "@schemas";
 import { canEncodeVideo } from "mediabunny";
 
 jest.mock("mediabunny", () => ({
@@ -36,12 +36,11 @@ const clip = (fields: Partial<ResolvedClip> & Pick<ResolvedClip, "asset">): Reso
 	...fields
 });
 
-function editWith(
-	clips: ResolvedClip[],
-	{ format = "mp4", duration = 5 }: { format?: string; duration?: number } = {}
-): Parameters<typeof findEditIssues>[0] {
+type EditOptions = { format?: string; duration?: number; output?: Partial<ResolvedEdit["output"]> };
+
+function editWith(clips: ResolvedClip[], { format = "mp4", duration = 5, output }: EditOptions = {}): Parameters<typeof findEditIssues>[0] {
 	return {
-		getResolvedEdit: () => ({ timeline: { tracks: [{ clips }] }, output: { format: "mp4" } }),
+		getResolvedEdit: () => ({ timeline: { tracks: [{ clips }] }, output: { format: "mp4", ...output } }),
 		getOutputFormat: () => format,
 		getFontUrlByFamilyAndWeight: (family: string, weight: number) => customFonts[`${family}|${weight}`] ?? null,
 		totalDuration: duration
@@ -50,7 +49,7 @@ function editWith(
 
 const HD_BITRATE = exportBitrate({ width: 1920, height: 1080 });
 
-const codes = (clips: ResolvedClip[], options?: { format?: string; duration?: number; bitrate?: number }): string[] =>
+const codes = (clips: ResolvedClip[], options?: EditOptions & { bitrate?: number }): string[] =>
 	findEditIssues(editWith(clips, options), options?.bitrate ?? HD_BITRATE).map(issue => issue.code);
 
 describe("findEditIssues", () => {
@@ -79,6 +78,11 @@ describe("findEditIssues", () => {
 		expect(codes([], { format: "gif" })).toEqual(["output-format"]);
 	});
 
+	it("reports a range or scaleTo as output-format, since the browser exports the whole timeline at the edit's size", () => {
+		expect(codes([], { output: { range: { start: 1, length: 2 } } })).toEqual(["output-format"]);
+		expect(codes([], { output: { scaleTo: "sd" } })).toEqual(["output-format"]);
+	});
+
 	it("reports chroma key as chroma-key", () => {
 		expect(codes([clip({ asset: { type: "video", src: "https://example.com/a.mp4", chromaKey: { color: "#00b140" } } })])).toEqual(["chroma-key"]);
 	});

From 9fa20897d2b7c57fffa02d0484c900c0b5f3029a Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:06:37 +1100
Subject: [PATCH 07/16] fix(export): check AAC encoding before mixing an edit's
 audio

---
 src/core/export/audio-processor.ts    |  4 ++++
 src/core/export/export-coordinator.ts | 14 ++++++++------
 src/core/export/export-preflight.ts   | 15 ++++++++++-----
 src/core/export/export-utils.ts       |  3 +++
 tests/export-coordinator.test.ts      | 24 ++++++++++++++++++++++--
 tests/export-preflight.test.ts        | 20 +++++++++++++++++---
 6 files changed, 64 insertions(+), 16 deletions(-)

diff --git a/src/core/export/audio-processor.ts b/src/core/export/audio-processor.ts
index d04b45a2..019087c1 100644
--- a/src/core/export/audio-processor.ts
+++ b/src/core/export/audio-processor.ts
@@ -26,6 +26,10 @@ interface AudioBearingClip {
  * Mixes every audio-bearing clip into one export track
  */
 export class AudioProcessor {
+	hasAudio(tracks: ReadonlyArray<ReadonlyArray<Player>>): boolean {
+		return this.collectClips(tracks).length > 0;
+	}
+
 	/** Decode and mix all audio-bearing clips into one buffer; null when there is no audio. */
 	async renderMix(tracks: ReadonlyArray<ReadonlyArray<Player>>, totalDuration: number): Promise<AudioBuffer | null> {
 		const clips = this.collectClips(tracks);
diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index cb91608d..f13a0e2c 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -7,7 +7,7 @@ import * as pixi from "pixi.js";
 import { AudioProcessor } from "./audio-processor";
 import { findBrowserIssue, findEditIssues } from "./export-preflight";
 import { ExportProgressUI } from "./export-progress-ui";
-import { ExportError, exportBitrate } from "./export-utils";
+import { AUDIO_BITRATE, ExportError, exportBitrate } from "./export-utils";
 import { VideoFrameProcessor } from "./video-frame-processor";
 
 interface ExportConfig {
@@ -16,6 +16,7 @@ interface ExportConfig {
 	bitrate: number;
 	frames: number;
 	frameDuration: number;
+	muted: boolean;
 }
 
 export interface ExportBlobOptions {
@@ -123,12 +124,11 @@ export class ExportCoordinator {
 			output.addVideoTrack(videoSource);
 
 			report(0.15, "Mixing audio...");
-			const muted = this.edit.getEdit().output?.mute === true;
-			const mixedAudio = muted ? null : await this.audioProcessor.renderMix(this.edit.getTracks(), this.edit.totalDuration);
+			const mixedAudio = cfg.muted ? null : await this.audioProcessor.renderMix(this.edit.getTracks(), this.edit.totalDuration);
 			throwIfAborted();
 			let audioSource: AudioBufferSource | null = null;
 			if (mixedAudio) {
-				audioSource = new AudioBufferSource({ codec: "aac", bitrate: 192_000 });
+				audioSource = new AudioBufferSource({ codec: "aac", bitrate: AUDIO_BITRATE });
 				output.addAudioTrack(audioSource);
 			}
 
@@ -166,7 +166,8 @@ export class ExportCoordinator {
 		await waitForLoads(this.edit, signal);
 
 		const issues = findEditIssues(this.edit, cfg.bitrate);
-		const browserIssue = await findBrowserIssue(cfg.size, cfg.bitrate);
+		const audio = !cfg.muted && this.audioProcessor.hasAudio(this.edit.getTracks());
+		const browserIssue = await findBrowserIssue(cfg.size, cfg.bitrate, audio);
 		if (browserIssue) issues.push(browserIssue);
 		issues.push(...(await this.videoProcessor.initialize(this.edit.getTracks().flat())));
 		if (issues.length > 0) {
@@ -266,7 +267,8 @@ export class ExportCoordinator {
 			size,
 			bitrate: exportBitrate(size),
 			frames: Math.ceil(this.edit.totalDuration * fps),
-			frameDuration: 1 / fps // seconds per frame
+			frameDuration: 1 / fps, // seconds per frame
+			muted: this.edit.getEdit().output?.mute === true
 		};
 	}
 }
diff --git a/src/core/export/export-preflight.ts b/src/core/export/export-preflight.ts
index b981238d..2b103620 100644
--- a/src/core/export/export-preflight.ts
+++ b/src/core/export/export-preflight.ts
@@ -6,9 +6,9 @@ import { NAMED_FONT_WEIGHTS } from "@core/fonts/font-weights";
 import { isPendingAiAsset } from "@core/shared/ai-asset-utils";
 import { inferAssetTypeFromUrl, isTextHtml } from "@core/shared/asset-utils";
 import type { ResolvedClip } from "@schemas";
-import { canEncodeVideo } from "mediabunny";
+import { canEncodeAudio, canEncodeVideo } from "mediabunny";
 
-import { exportBitrate, type ExportIssue, type ExportIssueCode } from "./export-utils";
+import { AUDIO_BITRATE, exportBitrate, type ExportIssue, type ExportIssueCode } from "./export-utils";
 
 /** The audio mix is held in memory until the export finishes, and it grows with length at any size. */
 export const MAX_EXPORT_SECONDS = 300;
@@ -85,7 +85,12 @@ export function findEditIssues(edit: PreflightEdit, bitrate: number): ExportIssu
 	return issues;
 }
 
-export async function findBrowserIssue(size: { width: number; height: number }, bitrate: number): Promise<ExportIssue | null> {
-	if (await canEncodeVideo("avc", { width: size.width, height: size.height, bitrate })) return null;
-	return { code: "browser", message: `This browser can't encode H.264 video at ${size.width}×${size.height}.` };
+export async function findBrowserIssue(size: { width: number; height: number }, bitrate: number, audio: boolean): Promise<ExportIssue | null> {
+	if (!(await canEncodeVideo("avc", { width: size.width, height: size.height, bitrate }))) {
+		return { code: "browser", message: `This browser can't encode H.264 video at ${size.width}×${size.height}.` };
+	}
+	// Asked before the mix, which can take a while, rather than failing once it's done.
+	if (audio && !(await canEncodeAudio("aac", { bitrate: AUDIO_BITRATE })))
+		return { code: "browser", message: "This browser can't encode AAC audio." };
+	return null;
 }
diff --git a/src/core/export/export-utils.ts b/src/core/export/export-utils.ts
index 8b499dac..7d5c7c9b 100644
--- a/src/core/export/export-utils.ts
+++ b/src/core/export/export-utils.ts
@@ -71,6 +71,9 @@ export class ExportError extends Error {
 	}
 }
 
+/** AAC bitrate for the mix, which is stereo at 48 kHz: the format canEncodeAudio checks by default. */
+export const AUDIO_BITRATE = 192_000;
+
 /**
  * 5 Mbps at 1920×1080 scaled by pixel count, so every output size gets the bits per pixel that 1080p
  * had, with a 1 Mbps floor: small outputs still carry text, which blurs first when starved.
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index fad8c6ba..22f6b9fa 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -6,7 +6,7 @@ import { ASSET_SETTLE_TIMEOUT_MS, ExportCoordinator } from "@core/export/export-
 import { ExportProgressUI } from "@core/export/export-progress-ui";
 import { ExportError, exportBitrate } from "@core/export/export-utils";
 import { calculateSizeFromPreset } from "@core/output-settings-manager";
-import { canEncodeVideo, CanvasSink, CanvasSource, Input, Output } from "mediabunny";
+import { canEncodeAudio, canEncodeVideo, CanvasSink, CanvasSource, Input, Output } from "mediabunny";
 
 const mockOutputs: Array<{ cancel: jest.Mock; addAudioTrack: jest.Mock; state: string }> = [];
 
@@ -37,6 +37,7 @@ jest.mock("mediabunny", () => ({
 	CanvasSource: jest.fn().mockImplementation(() => ({ add: jest.fn().mockResolvedValue(undefined) })),
 	AudioBufferSource: jest.fn().mockImplementation(() => ({ add: jest.fn().mockResolvedValue(undefined) })),
 	canEncodeVideo: jest.fn(),
+	canEncodeAudio: jest.fn(),
 	Input: jest.fn(),
 	UrlSource: jest.fn(),
 	CanvasSink: jest.fn(),
@@ -59,9 +60,10 @@ jest.mock("pixi.js", () => ({
 jest.mock("@shotstack/shotstack-canvas", () => ({ parseFontFamily: (family: string) => ({ family, weight: "400" }) }));
 
 const mockRenderMix = jest.fn();
+const mockHasAudio = jest.fn();
 
 jest.mock("../src/core/export/audio-processor", () => ({
-	AudioProcessor: jest.fn().mockImplementation(() => ({ renderMix: mockRenderMix }))
+	AudioProcessor: jest.fn().mockImplementation(() => ({ renderMix: mockRenderMix, hasAudio: mockHasAudio }))
 }));
 
 const SIZE = { width: 4, height: 2 };
@@ -118,6 +120,8 @@ beforeEach(() => {
 	jest.mocked(canEncodeVideo).mockResolvedValue(true);
 	jest.mocked(CanvasSource).mockClear();
 	mockRenderMix.mockReset().mockResolvedValue(null);
+	mockHasAudio.mockReset().mockReturnValue(false);
+	jest.mocked(canEncodeAudio).mockReset().mockResolvedValue(true);
 });
 
 describe("ExportCoordinator.exportBlob", () => {
@@ -313,6 +317,22 @@ describe("output settings", () => {
 		expect(mockOutputs[0].addAudioTrack).not.toHaveBeenCalled();
 		exporter.dispose();
 	});
+
+	it("refuses an edit with audio before mixing when the browser can't encode AAC, unless it's muted", async () => {
+		const { exporter, edit } = createHarness();
+		mockHasAudio.mockReturnValue(true);
+		jest.mocked(canEncodeAudio).mockResolvedValue(false);
+
+		const error = await exporter.exportBlob().catch((e: unknown) => e);
+
+		expect(error).toMatchObject({ phase: "unsupported" });
+		expect((error as ExportError).issues?.map(issue => issue.code)).toEqual(["browser"]);
+		expect(mockRenderMix).not.toHaveBeenCalled();
+
+		edit.getEdit.mockReturnValue({ output: { fps: 2, mute: true } });
+		await expect(exporter.exportBlob()).resolves.toBeInstanceOf(Blob);
+		exporter.dispose();
+	});
 });
 
 describe("off-screen export", () => {
diff --git a/tests/export-preflight.test.ts b/tests/export-preflight.test.ts
index 8e1690da..8f21ba35 100644
--- a/tests/export-preflight.test.ts
+++ b/tests/export-preflight.test.ts
@@ -3,10 +3,11 @@ import { exportBitrate } from "@core/export/export-utils";
 import { VideoFrameProcessor } from "@core/export/video-frame-processor";
 import { sec } from "@core/timing/types";
 import type { ResolvedClip, ResolvedEdit } from "@schemas";
-import { canEncodeVideo } from "mediabunny";
+import { canEncodeAudio, canEncodeVideo } from "mediabunny";
 
 jest.mock("mediabunny", () => ({
 	canEncodeVideo: jest.fn(),
+	canEncodeAudio: jest.fn(),
 	Input: jest.fn().mockImplementation(() => ({
 		getPrimaryVideoTrack: jest.fn().mockRejectedValue(new Error("Input has an unsupported or unrecognizable format.")),
 		dispose: jest.fn()
@@ -153,7 +154,7 @@ describe("findBrowserIssue", () => {
 	it("reports a browser that can't encode the output as browser", async () => {
 		jest.mocked(canEncodeVideo).mockResolvedValueOnce(false);
 
-		await expect(findBrowserIssue({ width: 1920, height: 1080 }, 5_000_000)).resolves.toEqual({
+		await expect(findBrowserIssue({ width: 1920, height: 1080 }, 5_000_000, false)).resolves.toEqual({
 			code: "browser",
 			message: "This browser can't encode H.264 video at 1920×1080."
 		});
@@ -163,7 +164,20 @@ describe("findBrowserIssue", () => {
 	it("reports nothing when the encoder accepts the config", async () => {
 		jest.mocked(canEncodeVideo).mockResolvedValueOnce(true);
 
-		await expect(findBrowserIssue({ width: 1280, height: 720 }, 2_222_222)).resolves.toBeNull();
+		await expect(findBrowserIssue({ width: 1280, height: 720 }, 2_222_222, false)).resolves.toBeNull();
+	});
+
+	it("reports a browser that can't encode AAC as browser when the edit has audio", async () => {
+		jest.mocked(canEncodeVideo).mockResolvedValue(true);
+		jest.mocked(canEncodeAudio).mockResolvedValue(false);
+
+		await expect(findBrowserIssue({ width: 1280, height: 720 }, 2_222_222, true)).resolves.toEqual({
+			code: "browser",
+			message: "This browser can't encode AAC audio."
+		});
+		jest.mocked(canEncodeAudio).mockClear();
+		await expect(findBrowserIssue({ width: 1280, height: 720 }, 2_222_222, false)).resolves.toBeNull();
+		expect(canEncodeAudio).not.toHaveBeenCalled();
 	});
 });
 

From 635d75da35764c17fedb860675a13fddecf83df8 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:07:24 +1100
Subject: [PATCH 08/16] fix(export): fail when an audio or speech clip's audio
 can't be loaded

---
 src/core/export/audio-processor.ts |  7 ++++++
 tests/export-audio.test.ts         | 38 +++++++++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/src/core/export/audio-processor.ts b/src/core/export/audio-processor.ts
index 019087c1..4b7172c2 100644
--- a/src/core/export/audio-processor.ts
+++ b/src/core/export/audio-processor.ts
@@ -3,6 +3,7 @@ import { createAnimatedSpeed } from "@canvas/players/video-player";
 import type { VideoAsset } from "@schemas";
 
 import { buildVolumeAutomation, type VolumeTween } from "./export-timing";
+import { ExportError } from "./export-utils";
 
 const OUTPUT_SAMPLE_RATE = 48_000;
 const OUTPUT_CHANNELS = 2;
@@ -13,6 +14,8 @@ const SPEED_STEP_SECONDS = 0.01;
 const AUDIO_BEARING = new Set<string>([PlayerType.Audio, PlayerType.Video, PlayerType.TextToSpeech]);
 
 interface AudioBearingClip {
+	clipId: string | null;
+	video: boolean;
 	src: string;
 	start: number;
 	length: number;
@@ -42,6 +45,8 @@ export class AudioProcessor {
 
 		for (const clip of clips) {
 			const buffer = await this.decode(clip.src, ctx, decodeCache);
+			// A video may have no audio track; an audio or speech clip without its audio would export silent.
+			if (!buffer && !clip.video) throw new ExportError("A clip's audio couldn't be loaded", "assets", { clipId: clip.clipId });
 			if (buffer) {
 				const source = ctx.createBufferSource();
 				source.buffer = buffer;
@@ -130,6 +135,8 @@ export class AudioProcessor {
 		if (typeof asset?.src !== "string" || !asset.src) return null;
 
 		return {
+			clipId: clip.clipId,
+			video: clip.playerType === PlayerType.Video,
 			src: asset.src,
 			start: clip.getStart(),
 			length: clip.getLength(),
diff --git a/tests/export-audio.test.ts b/tests/export-audio.test.ts
index 8278c228..20254d1d 100644
--- a/tests/export-audio.test.ts
+++ b/tests/export-audio.test.ts
@@ -26,7 +26,13 @@ function createBufferSource() {
 const createGain = () => ({ gain: { setValueAtTime: jest.fn(), linearRampToValueAtTime: jest.fn() }, connect: (node: unknown) => node });
 
 function mediaClip(playerType: PlayerType, asset: Record<string, unknown>, start: number, length: number): Player {
-	return { playerType, clipConfiguration: { asset }, getStart: () => start, getLength: () => length } as unknown as Player;
+	return {
+		clipId: `${playerType}-clip`,
+		playerType,
+		clipConfiguration: { asset },
+		getStart: () => start,
+		getLength: () => length
+	} as unknown as Player;
 }
 
 beforeAll(() => {
@@ -83,3 +89,33 @@ describe("AudioProcessor speed", () => {
 		expect(scheduled[0].stop).toEqual([[2.5]]);
 	});
 });
+
+describe("AudioProcessor failures", () => {
+	beforeEach(() => {
+		jest.spyOn(console, "warn").mockImplementation(() => undefined);
+	});
+
+	afterEach(() => {
+		jest.restoreAllMocks();
+	});
+
+	it("fails with phase assets, naming the clip, when an audio or speech clip's file can't be fetched or decoded", async () => {
+		jest.mocked(fetch).mockRejectedValueOnce(new TypeError("Failed to fetch"));
+		await expect(
+			new AudioProcessor().renderMix([[mediaClip(PlayerType.Audio, { type: "audio", src: "https://example.com/gone.mp3" }, 0, 4)]], 10)
+		).rejects.toMatchObject({ name: "ExportError", phase: "assets", context: { clipId: "audio-clip" } });
+
+		jest.mocked(fetch).mockResolvedValueOnce({ ok: false } as Response);
+		await expect(
+			new AudioProcessor().renderMix([[mediaClip(PlayerType.TextToSpeech, { type: "text-to-speech", src: "https://example.com/tts.mp3" }, 0, 4)]], 10)
+		).rejects.toMatchObject({ phase: "assets", context: { clipId: "text-to-speech-clip" } });
+	});
+
+	it("leaves a video without usable audio silent", async () => {
+		jest.mocked(fetch).mockResolvedValueOnce({ ok: false } as Response);
+
+		await expect(
+			new AudioProcessor().renderMix([[mediaClip(PlayerType.Video, { type: "video", src: "https://example.com/silent.mp4" }, 0, 4)]], 10)
+		).resolves.toBeNull();
+	});
+});

From bd2507f8797ab5de16d1c8ff41e226a30e05f5f4 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:08:04 +1100
Subject: [PATCH 09/16] fix(export): allow one export at a time per edit across
 exporters

---
 src/core/export/export-coordinator.ts | 14 ++++++++------
 tests/export-coordinator.test.ts      | 12 ++++++++++++
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index f13a0e2c..99494e54 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -31,6 +31,9 @@ export const ASSET_SETTLE_TIMEOUT_MS = 30_000;
 
 const cancelled = (): ExportError => new ExportError("Export cancelled", "cancelled");
 
+// Per edit, not per exporter: two exports of one edit would both move its playhead and swap its video textures.
+const exporting = new WeakSet<Edit>();
+
 // A stalled asset request can keep a load pending indefinitely, so the wait is bounded and a cancel ends it early.
 function waitForLoads(edit: Pick<Edit, "whenSettled" | "getLoadingClipIds">, signal?: AbortSignal): Promise<void> {
 	let timer: ReturnType<typeof setTimeout> | undefined;
@@ -53,7 +56,6 @@ function waitForLoads(edit: Pick<Edit, "whenSettled" | "getLoadingClipIds">, sig
 export class ExportCoordinator {
 	private readonly edit: Edit;
 	private readonly app: pixi.Application;
-	private isExporting = false;
 	private videoProcessor = new VideoFrameProcessor();
 	private audioProcessor = new AudioProcessor();
 	private progressUI = new ExportProgressUI();
@@ -69,7 +71,7 @@ export class ExportCoordinator {
 	}
 
 	async export(filename = "shotstack-export.mp4", fps?: number): Promise<void> {
-		if (this.isExporting) throw new ExportError("Export in progress", "init");
+		if (exporting.has(this.edit)) throw new ExportError("Export in progress", "init");
 
 		this.progressUI.create();
 		try {
@@ -95,14 +97,14 @@ export class ExportCoordinator {
 	}
 
 	private async encode(fps: number, { signal, onProgress }: ExportBlobOptions): Promise<Blob> {
-		if (this.isExporting) throw new ExportError("Export in progress", "init");
+		if (exporting.has(this.edit)) throw new ExportError("Export in progress", "init");
 		const throwIfAborted = (): void => {
 			if (signal?.aborted) throw cancelled();
 		};
 		throwIfAborted();
 		const report: Progress = (fraction, stage) => onProgress?.(fraction, stage);
 
-		this.isExporting = true;
+		exporting.add(this.edit);
 		let output: Output | undefined;
 
 		try {
@@ -156,7 +158,7 @@ export class ExportCoordinator {
 			}
 			throw error instanceof ExportError ? error : new ExportError(`Export failed: ${error}`, "export");
 		} finally {
-			this.isExporting = false;
+			exporting.delete(this.edit);
 			// Releases decoders the checks opened when the export stops before drawing a frame.
 			this.videoProcessor.restore();
 		}
@@ -246,7 +248,7 @@ export class ExportCoordinator {
 
 	private handleKeyDown = (e: KeyboardEvent): void => {
 		if (e.target instanceof HTMLInputElement || e.target instanceof HTMLTextAreaElement) return;
-		if (e.code === "KeyE" && (e.metaKey || e.ctrlKey) && !this.isExporting) {
+		if (e.code === "KeyE" && (e.metaKey || e.ctrlKey) && !exporting.has(this.edit)) {
 			e.preventDefault();
 			this.export("shotstack-export.mp4", this.edit.getEdit().output?.fps || 30).catch(err => console.error("Export failed:", err));
 		}
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index 22f6b9fa..615fcddd 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -303,6 +303,18 @@ describe("ExportCoordinator.exportBlob", () => {
 		await first;
 		exporter.dispose();
 	});
+
+	it("refuses a second exporter on the same edit while one is running", async () => {
+		const { exporter, edit, app } = createHarness();
+		const second = new ExportCoordinator(edit as unknown as Edit, { application: app } as unknown as Canvas);
+		const first = exporter.exportBlob();
+
+		await expect(second.exportBlob()).rejects.toMatchObject({ phase: "init", message: "Export in progress" });
+		await first;
+		await expect(second.exportBlob()).resolves.toBeInstanceOf(Blob);
+		exporter.dispose();
+		second.dispose();
+	});
 });
 
 describe("output settings", () => {

From e3deac161d8867e0e5e20e672db49a153ba65d98 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:09:41 +1100
Subject: [PATCH 10/16] fix(export): let a cancel win and end the checks and
 audio mix promptly

---
 src/core/export/export-coordinator.ts    | 31 ++++++++------
 src/core/export/video-frame-processor.ts |  4 +-
 tests/export-coordinator.test.ts         | 54 ++++++++++++++++++++++++
 tests/export-video-frames.test.ts        | 25 +++++++++++
 4 files changed, 101 insertions(+), 13 deletions(-)

diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index 99494e54..c13673ec 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -34,23 +34,27 @@ const cancelled = (): ExportError => new ExportError("Export cancelled", "cancel
 // Per edit, not per exporter: two exports of one edit would both move its playhead and swap its video textures.
 const exporting = new WeakSet<Edit>();
 
+// Rejects as soon as the signal aborts; the work itself runs on and its result is ignored.
+function untilAborted<T>(work: Promise<T>, signal?: AbortSignal): Promise<T> {
+	let onAbort = (): void => {};
+	const aborted = new Promise<never>((_, reject) => {
+		onAbort = () => reject(cancelled());
+		if (signal?.aborted) onAbort();
+		else signal?.addEventListener("abort", onAbort, { once: true });
+	});
+	return Promise.race([work, aborted]).finally(() => signal?.removeEventListener("abort", onAbort));
+}
+
 // A stalled asset request can keep a load pending indefinitely, so the wait is bounded and a cancel ends it early.
 function waitForLoads(edit: Pick<Edit, "whenSettled" | "getLoadingClipIds">, signal?: AbortSignal): Promise<void> {
 	let timer: ReturnType<typeof setTimeout> | undefined;
-	let onAbort = (): void => {};
-	const stopped = new Promise<never>((_, reject) => {
+	const timedOut = new Promise<never>((_, reject) => {
 		timer = setTimeout(() => {
 			const [clipId] = edit.getLoadingClipIds();
 			reject(new ExportError(`A clip's asset didn't finish loading within ${ASSET_SETTLE_TIMEOUT_MS / 1000} seconds`, "assets", { clipId }));
 		}, ASSET_SETTLE_TIMEOUT_MS);
-		onAbort = () => reject(cancelled());
-		if (signal?.aborted) onAbort();
-		else signal?.addEventListener("abort", onAbort, { once: true });
-	});
-	return Promise.race([edit.whenSettled(), stopped]).finally(() => {
-		clearTimeout(timer);
-		signal?.removeEventListener("abort", onAbort);
 	});
+	return untilAborted(Promise.race([edit.whenSettled(), timedOut]), signal).finally(() => clearTimeout(timer));
 }
 
 export class ExportCoordinator {
@@ -126,7 +130,7 @@ export class ExportCoordinator {
 			output.addVideoTrack(videoSource);
 
 			report(0.15, "Mixing audio...");
-			const mixedAudio = cfg.muted ? null : await this.audioProcessor.renderMix(this.edit.getTracks(), this.edit.totalDuration);
+			const mixedAudio = cfg.muted ? null : await untilAborted(this.audioProcessor.renderMix(this.edit.getTracks(), this.edit.totalDuration), signal);
 			throwIfAborted();
 			let audioSource: AudioBufferSource | null = null;
 			if (mixedAudio) {
@@ -145,6 +149,7 @@ export class ExportCoordinator {
 			await this.processFrames(cfg, videoSource, ctx, report, throwIfAborted);
 
 			await output.finalize();
+			throwIfAborted();
 
 			const data = (output.target as BufferTarget).buffer;
 			if (!data) throw new Error("No video data");
@@ -156,6 +161,8 @@ export class ExportCoordinator {
 				// A failed cancel must not replace the error that stopped the export.
 				await output.cancel().catch(() => {});
 			}
+			// The host asked to stop, so an error that races the cancel still reports as cancelled.
+			if (signal?.aborted) throw cancelled();
 			throw error instanceof ExportError ? error : new ExportError(`Export failed: ${error}`, "export");
 		} finally {
 			exporting.delete(this.edit);
@@ -169,9 +176,9 @@ export class ExportCoordinator {
 
 		const issues = findEditIssues(this.edit, cfg.bitrate);
 		const audio = !cfg.muted && this.audioProcessor.hasAudio(this.edit.getTracks());
-		const browserIssue = await findBrowserIssue(cfg.size, cfg.bitrate, audio);
+		const browserIssue = await untilAborted(findBrowserIssue(cfg.size, cfg.bitrate, audio), signal);
 		if (browserIssue) issues.push(browserIssue);
-		issues.push(...(await this.videoProcessor.initialize(this.edit.getTracks().flat())));
+		issues.push(...(await untilAborted(this.videoProcessor.initialize(this.edit.getTracks().flat(), signal), signal)));
 		if (issues.length > 0) {
 			throw new ExportError("This edit can't be exported in the browser", "unsupported", {}, undefined, issues);
 		}
diff --git a/src/core/export/video-frame-processor.ts b/src/core/export/video-frame-processor.ts
index c7c674dc..2cc5c2aa 100644
--- a/src/core/export/video-frame-processor.ts
+++ b/src/core/export/video-frame-processor.ts
@@ -39,7 +39,7 @@ export class VideoFrameProcessor {
 	private paused = new Set<VideoPlayerExtended>();
 
 	/** Open a decoder per video clip; a source the browser can't decode comes back as an issue. */
-	async initialize(clips: ReadonlyArray<unknown>): Promise<ExportIssue[]> {
+	async initialize(clips: ReadonlyArray<unknown>, signal?: AbortSignal): Promise<ExportIssue[]> {
 		const players = clips.filter(isVideoPlayer);
 		const issues: ExportIssue[] = [];
 
@@ -53,6 +53,8 @@ export class VideoFrameProcessor {
 					const track = await input.getPrimaryVideoTrack();
 					if (!track) return;
 					if (!(await track.canDecode())) throw new Error("No decoder for this codec");
+					// A cancelled export stops waiting for its probes and cleans up, so a late one cleans up after itself.
+					if (signal?.aborted) return;
 					this.decoders.set(player, {
 						input,
 						track,
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index 615fcddd..6b2d7d18 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -295,6 +295,60 @@ describe("ExportCoordinator.exportBlob", () => {
 		exporter.dispose();
 	});
 
+	it("rejects with phase cancelled promptly when aborted during the audio mix", async () => {
+		const { exporter } = createHarness();
+		const controller = new AbortController();
+		mockRenderMix.mockImplementation(() => {
+			queueMicrotask(() => controller.abort());
+			return new Promise(() => {});
+		});
+
+		const outcome = await Promise.race([
+			exporter.exportBlob({ signal: controller.signal }).catch((e: unknown) => e),
+			new Promise(resolve => {
+				setTimeout(() => resolve("still mixing"), 50);
+			})
+		]);
+
+		expect(outcome).toMatchObject({ phase: "cancelled" });
+		exporter.dispose();
+	});
+
+	it("reports a failure that follows an abort as cancelled", async () => {
+		const { exporter } = createHarness();
+		const controller = new AbortController();
+		const construct = jest.mocked(Output).getMockImplementation() as unknown as (...a: unknown[]) => { start: jest.Mock };
+		jest.mocked(Output).mockImplementationOnce((...args: unknown[]) => {
+			const output = construct(...args);
+			output.start.mockImplementation(async () => {
+				controller.abort();
+				throw new Error("muxer stopped");
+			});
+			return output as never;
+		});
+
+		await expect(exporter.exportBlob({ signal: controller.signal })).rejects.toMatchObject({ phase: "cancelled" });
+		exporter.dispose();
+	});
+
+	it("rejects with phase cancelled when aborted while the file is finalised", async () => {
+		const { exporter } = createHarness();
+		const controller = new AbortController();
+		const construct = jest.mocked(Output).getMockImplementation() as unknown as (...a: unknown[]) => { finalize: jest.Mock };
+		jest.mocked(Output).mockImplementationOnce((...args: unknown[]) => {
+			const output = construct(...args);
+			const finalize = output.finalize.getMockImplementation() as () => Promise<void>;
+			output.finalize.mockImplementation(async () => {
+				await finalize();
+				controller.abort();
+			});
+			return output as never;
+		});
+
+		await expect(exporter.exportBlob({ signal: controller.signal })).rejects.toMatchObject({ phase: "cancelled" });
+		exporter.dispose();
+	});
+
 	it("refuses a second export while one is running", async () => {
 		const { exporter } = createHarness();
 		const first = exporter.exportBlob();
diff --git a/tests/export-video-frames.test.ts b/tests/export-video-frames.test.ts
index c88074f9..67750d25 100644
--- a/tests/export-video-frames.test.ts
+++ b/tests/export-video-frames.test.ts
@@ -55,6 +55,31 @@ describe("VideoFrameProcessor", () => {
 		expect(dispose).toHaveBeenCalledTimes(1);
 	});
 
+	it("releases a decoder that opens after a cancelled export has cleaned up", async () => {
+		const dispose = jest.fn();
+		let openTrack = (): void => {};
+		jest.mocked(Input).mockImplementationOnce(
+			() =>
+				({
+					getPrimaryVideoTrack: () =>
+						new Promise(resolve => {
+							openTrack = () => resolve({ canDecode: async () => true });
+						}),
+					dispose
+				}) as unknown as InstanceType<typeof Input>
+		);
+		const processor = new VideoFrameProcessor();
+		const controller = new AbortController();
+
+		const probing = processor.initialize([videoPlayer()], controller.signal);
+		controller.abort();
+		processor.restore();
+		openTrack();
+		await probing;
+
+		expect(dispose).toHaveBeenCalledTimes(1);
+	});
+
 	it("restarts every paused video player, including one that got no decoder", () => {
 		const processor = new VideoFrameProcessor();
 		const player = videoPlayer("");

From 8b14f184ba684bd71dd7d33c7f72737ae5a0d335 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:11:33 +1100
Subject: [PATCH 11/16] fix(export): stop the export when the edit or playback
 changes mid-export

---
 readme.md                             |  2 +-
 src/core/export/export-coordinator.ts | 31 +++++++++++++----
 tests/export-coordinator.test.ts      | 49 +++++++++++++++++++++++++--
 3 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/readme.md b/readme.md
index 65a9077b..a367a467 100644
--- a/readme.md
+++ b/readme.md
@@ -337,7 +337,7 @@ const exporter = new VideoExporter(edit, canvas);
 await exporter.export("my-video.mp4", 25);
 ```
 
-`exportBlob()` runs the same export without the progress overlay or the download and resolves with the MP4 `Blob`. `onProgress` receives a fraction from 0 to 1 and a stage label. Aborting the signal rejects with an `ExportError` whose `phase` is `cancelled`.
+`exportBlob()` runs the same export without the progress overlay or the download and resolves with the MP4 `Blob`. `onProgress` receives a fraction from 0 to 1 and a stage label. Aborting the signal rejects with an `ExportError` whose `phase` is `cancelled`. The editor stays live while an export runs, but changing the edit, or playing, pausing or seeking, rejects the export with `phase` `export`.
 
 ```typescript
 import { ExportError } from "@shotstack/shotstack-studio";
diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index c13673ec..2aa3aff3 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -1,5 +1,6 @@
 import { Canvas } from "@canvas/shotstack-canvas";
 import { Edit } from "@core/edit-session";
+import { EditEvent } from "@core/events/edit-events";
 import { sec } from "@core/timing/types";
 import { Output, Mp4OutputFormat, BufferTarget, CanvasSource, AudioBufferSource } from "mediabunny";
 import * as pixi from "pixi.js";
@@ -110,6 +111,16 @@ export class ExportCoordinator {
 
 		exporting.add(this.edit);
 		let output: Output | undefined;
+		let changed = false;
+		const markChanged = (): void => {
+			changed = true;
+		};
+		const stopWatching = this.edit.events.on(EditEvent.EditChanged, markChanged);
+		// The editor stays live during export; anything checked, mixed or drawn before a change no longer matches the edit.
+		const throwIfStopped = (): void => {
+			throwIfAborted();
+			if (changed) throw new ExportError("The edit or playback changed during export", "export");
+		};
 
 		try {
 			output = new Output({ format: new Mp4OutputFormat(), target: new BufferTarget() });
@@ -117,7 +128,7 @@ export class ExportCoordinator {
 			report(0, "Preparing...");
 
 			await this.checkExportable(cfg, signal);
-			throwIfAborted();
+			throwIfStopped();
 			report(0.1, "Video ready");
 
 			const canvas = document.createElement("canvas");
@@ -131,7 +142,7 @@ export class ExportCoordinator {
 
 			report(0.15, "Mixing audio...");
 			const mixedAudio = cfg.muted ? null : await untilAborted(this.audioProcessor.renderMix(this.edit.getTracks(), this.edit.totalDuration), signal);
-			throwIfAborted();
+			throwIfStopped();
 			let audioSource: AudioBufferSource | null = null;
 			if (mixedAudio) {
 				audioSource = new AudioBufferSource({ codec: "aac", bitrate: AUDIO_BITRATE });
@@ -146,7 +157,7 @@ export class ExportCoordinator {
 			}
 
 			report(0.25, "Exporting...");
-			await this.processFrames(cfg, videoSource, ctx, report, throwIfAborted);
+			await this.processFrames(cfg, videoSource, ctx, report, throwIfStopped, markChanged);
 
 			await output.finalize();
 			throwIfAborted();
@@ -165,6 +176,7 @@ export class ExportCoordinator {
 			if (signal?.aborted) throw cancelled();
 			throw error instanceof ExportError ? error : new ExportError(`Export failed: ${error}`, "export");
 		} finally {
+			stopWatching();
 			exporting.delete(this.edit);
 			// Releases decoders the checks opened when the export stops before drawing a frame.
 			this.videoProcessor.restore();
@@ -196,7 +208,8 @@ export class ExportCoordinator {
 		videoSource: CanvasSource,
 		ctx: CanvasRenderingContext2D,
 		report: Progress,
-		throwIfAborted: () => void
+		throwIfStopped: () => void,
+		onPlayback: () => void
 	): Promise<void> {
 		const container = this.edit.getViewportContainer();
 		const clips = this.edit.getTracks().flat();
@@ -206,13 +219,16 @@ export class ExportCoordinator {
 		// frame it drew, so the user never sees those moves; extract renders off-screen either way.
 		const tickerWasRunning = this.app.ticker.started;
 		this.app.stop();
+		const stopWatching: Array<() => void> = [];
 
 		try {
 			this.edit.pause();
+			// From here the export owns the playhead, so a play, pause or seek by anyone else stops it.
+			stopWatching.push(this.edit.events.on(EditEvent.PlaybackPlay, onPlayback), this.edit.events.on(EditEvent.PlaybackPause, onPlayback));
 			const players = this.videoProcessor.disableVideoPlayback(clips);
 
 			for (let i = 0; i < cfg.frames; i += 1) {
-				throwIfAborted();
+				throwIfStopped();
 				const frameTime = i * cfg.frameDuration;
 				this.edit.playbackTime = sec(frameTime);
 
@@ -228,6 +244,7 @@ export class ExportCoordinator {
 					}
 				}
 
+				throwIfStopped();
 				// pixi renders the container into a texture with its own transform swapped for the frame's,
 				// so the editor's pan and zoom never reach these pixels; resolution pins them to output pixels.
 				const pixels = this.app.renderer.extract.pixels({
@@ -245,7 +262,9 @@ export class ExportCoordinator {
 				report(0.25 + ((i + 1) / cfg.frames) * 0.75, "Exporting...");
 			}
 		} finally {
-			// First, so a throw while restoring playback can't leave the editor frozen. start() only schedules a frame.
+			// Restoring the playhead below seeks, which must not count as a change.
+			for (const stop of stopWatching) stop();
+			// Before restoring playback, so a throw there can't leave the editor frozen. start() only schedules a frame.
 			if (tickerWasRunning) this.app.start();
 			this.videoProcessor.restore();
 			this.edit.seek(sec(playbackTime));
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index 6b2d7d18..0f86c3f9 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -2,6 +2,8 @@
 
 import type { Canvas } from "@canvas/shotstack-canvas";
 import type { Edit } from "@core/edit-session";
+import { EditEvent, type EditEventMap } from "@core/events/edit-events";
+import { EventEmitter } from "@core/events/event-emitter";
 import { ASSET_SETTLE_TIMEOUT_MS, ExportCoordinator } from "@core/export/export-coordinator";
 import { ExportProgressUI } from "@core/export/export-progress-ui";
 import { ExportError, exportBitrate } from "@core/export/export-utils";
@@ -70,7 +72,9 @@ const SIZE = { width: 4, height: 2 };
 
 function createHarness() {
 	const viewport = { position: { x: 120, y: 80 }, scale: { x: 0.5, y: 0.5 }, visible: true };
+	const events = new EventEmitter<EditEventMap>();
 	const edit = {
+		events,
 		isPlaying: false,
 		playbackTime: 1.5,
 		totalDuration: 1,
@@ -87,9 +91,10 @@ function createHarness() {
 		setExportMode: jest.fn(),
 		executeEditCommand: jest.fn(),
 		getViewportContainer: () => viewport,
-		pause: jest.fn(),
-		play: jest.fn(),
-		seek: jest.fn()
+		// Like the editor's own: seeking pauses, and both report it.
+		pause: jest.fn(() => events.emit(EditEvent.PlaybackPause)),
+		play: jest.fn(() => events.emit(EditEvent.PlaybackPlay)),
+		seek: jest.fn((): void => edit.pause())
 	};
 	const viewAtExtract: Array<typeof viewport> = [];
 	const renderer = {
@@ -401,6 +406,44 @@ describe("output settings", () => {
 	});
 });
 
+describe("changes during export", () => {
+	const listenersOn = (events: EventEmitter<EditEventMap>): string[] => Object.keys((events as unknown as { events: object }).events);
+
+	it.each([
+		["the playhead is moved", (edit: { seek: (time: number) => void }) => edit.seek(0.25)],
+		["the edit changes", (edit: { events: EventEmitter<EditEventMap> }) => edit.events.emit(EditEvent.EditChanged, { source: "test", timestamp: 0 })]
+	])("rejects with phase export when %s between frames, leaving nothing subscribed", async (_, change) => {
+		const { exporter, edit, renderer } = createHarness();
+		jest.mocked(CanvasSource).mockImplementationOnce(() => ({ add: jest.fn(async () => change(edit)) }) as unknown as CanvasSource);
+
+		await expect(exporter.exportBlob()).rejects.toMatchObject({ phase: "export", message: "The edit or playback changed during export" });
+		expect(renderer.extract.pixels).toHaveBeenCalledTimes(1);
+		expect(listenersOn(edit.events)).toEqual([]);
+		exporter.dispose();
+	});
+
+	it("rejects when the edit changes while the audio mixes", async () => {
+		const { exporter, edit } = createHarness();
+		mockRenderMix.mockImplementation(async () => {
+			edit.events.emit(EditEvent.EditChanged, { source: "test", timestamp: 0 });
+			return null;
+		});
+
+		await expect(exporter.exportBlob()).rejects.toMatchObject({ phase: "export" });
+		expect(listenersOn(edit.events)).toEqual([]);
+		exporter.dispose();
+	});
+
+	it("isn't stopped by its own pause and restore, and leaves nothing subscribed", async () => {
+		const { exporter, edit } = createHarness();
+		edit.isPlaying = true;
+
+		await expect(exporter.exportBlob()).resolves.toBeInstanceOf(Blob);
+		expect(listenersOn(edit.events)).toEqual([]);
+		exporter.dispose();
+	});
+});
+
 describe("off-screen export", () => {
 	it("draws each frame from the viewport container at output size while the view stays where the user left it", async () => {
 		const { exporter, edit, renderer, viewport, viewAtExtract } = createHarness();

From 5d16c92bd65f8039d54c89e93016a724a573488f Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:13:43 +1100
Subject: [PATCH 12/16] fix(export): finish rich text and caption draws before
 reading each frame

---
 src/core/export/export-coordinator.ts | 29 +++++++++++++---------
 tests/export-coordinator.test.ts      | 35 +++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 12 deletions(-)

diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index 2aa3aff3..996a0a8d 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -244,18 +244,23 @@ export class ExportCoordinator {
 					}
 				}
 
-				throwIfStopped();
-				// pixi renders the container into a texture with its own transform swapped for the frame's,
-				// so the editor's pan and zoom never reach these pixels; resolution pins them to output pixels.
-				const pixels = this.app.renderer.extract.pixels({
-					target: container,
-					frame: new pixi.Rectangle(0, 0, cfg.size.width, cfg.size.height),
-					resolution: 1
-				});
-
-				const imageData = new ImageData(new Uint8ClampedArray(pixels.pixels), pixels.width, pixels.height);
-
-				ctx.putImageData(imageData, 0, 0);
+				// update() only starts rich text and caption draws; finish this frame's before reading pixels.
+				const active = clips.filter(clip => clip.isActive());
+				await Promise.all(active.map(clip => clip.prepareStaticRender()));
+				try {
+					throwIfStopped();
+					// pixi renders the container into a texture with its own transform swapped for the frame's,
+					// so the editor's pan and zoom never reach these pixels; resolution pins them to output pixels.
+					const pixels = this.app.renderer.extract.pixels({
+						target: container,
+						frame: new pixi.Rectangle(0, 0, cfg.size.width, cfg.size.height),
+						resolution: 1
+					});
+
+					ctx.putImageData(new ImageData(new Uint8ClampedArray(pixels.pixels), pixels.width, pixels.height), 0, 0);
+				} finally {
+					for (const clip of active) clip.endStaticRender();
+				}
 
 				await videoSource.add(i / cfg.fps, 1 / cfg.fps);
 
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index 0f86c3f9..de6cadbd 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -486,6 +486,35 @@ describe("off-screen export", () => {
 	});
 });
 
+describe("asynchronous drawing", () => {
+	it("finishes each active clip's draw before extracting its frame, and ends it after", async () => {
+		const { exporter, edit, renderer } = createHarness();
+		const order: string[] = [];
+		const title = {
+			clipId: "title",
+			needsResolution: false,
+			update: jest.fn(),
+			isActive: () => edit.playbackTime >= 0.5,
+			prepareStaticRender: jest.fn(async () => {
+				await Promise.resolve();
+				order.push(`drawn at ${edit.playbackTime}`);
+			}),
+			endStaticRender: jest.fn(() => order.push("ended"))
+		};
+		edit.tracks = [[title]];
+		const extract = renderer.extract.pixels.getMockImplementation()!;
+		renderer.extract.pixels.mockImplementation(() => {
+			order.push("extracted");
+			return extract();
+		});
+
+		await exporter.exportBlob();
+
+		expect(order).toEqual(["extracted", "drawn at 0.5", "extracted", "ended"]);
+		exporter.dispose();
+	});
+});
+
 describe("speed", () => {
 	it("decodes each video frame at the player's own source time for that frame", async () => {
 		const { exporter, edit } = createHarness();
@@ -518,6 +547,12 @@ describe("speed", () => {
 			getEnd(): number {
 				return this.start + this.length;
 			}
+
+			isActive = jest.fn(() => true);
+
+			prepareStaticRender = jest.fn(async () => {});
+
+			endStaticRender = jest.fn();
 		}
 		edit.tracks = [[new VideoPlayer(edit)]];
 		const getCanvas = jest.fn(async () => ({ canvas: { width: 2, height: 2 } }));

From a370aff069a2b38eaca7a95e203ca444b8d32641 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:14:44 +1100
Subject: [PATCH 13/16] docs(export): name the export phases and option types,
 and describe the checks plainly

---
 readme.md                       | 8 ++++----
 src/core/export/export-utils.ts | 6 +++++-
 src/core/export/index.ts        | 3 ++-
 src/index.ts                    | 2 +-
 tests/export-timing.test.ts     | 9 ---------
 5 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/readme.md b/readme.md
index a367a467..a5382cb3 100644
--- a/readme.md
+++ b/readme.md
@@ -354,7 +354,7 @@ const file = await exporter
   });
 ```
 
-Before encoding, both methods check that the browser can draw the edit the way a cloud render would. If it can't, they reject with an `ExportError` whose `phase` is `unsupported` and whose `issues` list each problem as `{ code, message, clipId? }`. `clipId` is the clip's `id` as returned by `edit.getEdit({ includeIds: true })`. A clip that failed to load, or whose asset is still loading after 30 seconds, rejects with `phase` `assets` and its `clipId` in `context`.
+Before encoding, both methods check the edit for features the browser is known to draw differently from a cloud render. If they find any, they reject with an `ExportError` whose `phase` is `unsupported` and whose `issues` list each problem as `{ code, message, clipId? }`. `clipId` is the clip's `id` as returned by `edit.getEdit({ includeIds: true })`. A clip that failed to load, or whose asset is still loading after 30 seconds, rejects with `phase` `assets` and its `clipId` in `context`. Starting an export while another export of the same edit runs rejects with `phase` `init`, and a failure while encoding rejects with `phase` `export`.
 
 | Code | Reason |
 | --- | --- |
@@ -366,10 +366,10 @@ Before encoding, both methods check that the browser can draw the edit the way a
 | `html` | An `html` clip that isn't the plain text form, or any `html5` clip |
 | `effect` | An effect without a preset in the editor |
 | `transition` | A transition without a preset in the editor |
-| `font` | A font that is neither built in nor listed in `timeline.fonts` |
+| `font` | A font that is neither built in (including the Google catalogue) nor loaded with the edit's `timeline.fonts` |
 | `luma` | A luma matte whose source is a video |
-| `too-long` | The edit runs longer than five minutes, or less above 1080p (75 seconds at 4K) |
-| `browser` | The browser can't encode H.264 at the output size |
+| `too-long` | The edit runs longer than five minutes, or than the shorter limit for sizes above 1080p (75 seconds at 4K) |
+| `browser` | The browser can't encode H.264 at the output size, or AAC when the edit has audio |
 
 ## Merge Fields
 
diff --git a/src/core/export/export-utils.ts b/src/core/export/export-utils.ts
index 7d5c7c9b..38677b27 100644
--- a/src/core/export/export-utils.ts
+++ b/src/core/export/export-utils.ts
@@ -54,13 +54,17 @@ export interface ExportIssue {
 	clipId?: string;
 }
 
+/** Where an export stopped; `unknown` when an `ExportError` is built without one. */
+export type ExportPhase = "init" | "assets" | "unsupported" | "export" | "cancelled" | "unknown";
+
 /**
  * Export error with context
  */
 export class ExportError extends Error {
 	constructor(
 		message: string,
-		public readonly phase: string = "unknown",
+		// `string & {}` accepts any string while editors still suggest the known phases.
+		public readonly phase: ExportPhase | (string & {}) = "unknown",
 		public readonly context: Record<string, unknown> = {},
 		cause?: Error,
 		public readonly issues?: ExportIssue[]
diff --git a/src/core/export/index.ts b/src/core/export/index.ts
index 4e90329a..49599ce8 100644
--- a/src/core/export/index.ts
+++ b/src/core/export/index.ts
@@ -4,6 +4,7 @@
 
 // Export main coordinator as VideoExporter for backward compatibility
 export { ExportCoordinator as VideoExporter } from "./export-coordinator";
+export type { ExportBlobOptions } from "./export-coordinator";
 
 // Export processors
 export { VideoFrameProcessor } from "./video-frame-processor";
@@ -11,7 +12,7 @@ export { AudioProcessor } from "./audio-processor";
 
 // Export utilities and errors
 export { SimpleLRUCache, ExportError } from "./export-utils";
-export type { ExportIssue, ExportIssueCode } from "./export-utils";
+export type { ExportIssue, ExportIssueCode, ExportPhase } from "./export-utils";
 
 // Export UI component
 export { ExportProgressUI } from "./export-progress-ui";
diff --git a/src/index.ts b/src/index.ts
index 2b7b3bb3..86f3c91f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -4,7 +4,7 @@ export { Edit } from "@core/edit-session";
 export { Canvas } from "@canvas/shotstack-canvas";
 export { Controls } from "@core/inputs/controls";
 export { VideoExporter, ExportError } from "@core/export";
-export type { ExportIssue, ExportIssueCode } from "@core/export";
+export type { ExportBlobOptions, ExportIssue, ExportIssueCode, ExportPhase } from "@core/export";
 export { Timeline } from "@timeline/index";
 export { UIController } from "@core/ui/ui-controller";
 export { WebGLUnsupportedError } from "@core/webgl-support";
diff --git a/tests/export-timing.test.ts b/tests/export-timing.test.ts
index f8bf44c3..422bddbc 100644
--- a/tests/export-timing.test.ts
+++ b/tests/export-timing.test.ts
@@ -1,12 +1,3 @@
-/**
- * Regression tests for export timing math.
- *
- * The export module historically treated the canvas players' second-based
- * timings as milliseconds, dividing by 1000 in three places. That froze
- * exported video on its first frame and truncated audio to ~0.1% of its
- * length. These tests pin the units to seconds so the regression cannot recur.
- */
-
 import { buildVolumeAutomation } from "../src/core/export/export-timing";
 
 describe("buildVolumeAutomation", () => {

From 6511a097e93b084235c60beb0f557d7230dab23c Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:16:17 +1100
Subject: [PATCH 14/16] fix(export): keep decoded video textures out of pixi's
 texture cache

---
 src/core/export/export-preflight.ts      | 5 +++--
 src/core/export/video-frame-processor.ts | 3 ++-
 tests/export-coordinator.test.ts         | 6 ++----
 tests/export-video-frames.test.ts        | 6 ++----
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/src/core/export/export-preflight.ts b/src/core/export/export-preflight.ts
index 2b103620..9f9da3f7 100644
--- a/src/core/export/export-preflight.ts
+++ b/src/core/export/export-preflight.ts
@@ -89,8 +89,9 @@ export async function findBrowserIssue(size: { width: number; height: number },
 	if (!(await canEncodeVideo("avc", { width: size.width, height: size.height, bitrate }))) {
 		return { code: "browser", message: `This browser can't encode H.264 video at ${size.width}×${size.height}.` };
 	}
-	// Asked before the mix, which can take a while, rather than failing once it's done.
-	if (audio && !(await canEncodeAudio("aac", { bitrate: AUDIO_BITRATE })))
+	// Asked up front: the encoder is first needed after the audio mix, which can take a while.
+	if (audio && !(await canEncodeAudio("aac", { bitrate: AUDIO_BITRATE }))) {
 		return { code: "browser", message: "This browser can't encode AAC audio." };
+	}
 	return null;
 }
diff --git a/src/core/export/video-frame-processor.ts b/src/core/export/video-frame-processor.ts
index 2cc5c2aa..f3527779 100644
--- a/src/core/export/video-frame-processor.ts
+++ b/src/core/export/video-frame-processor.ts
@@ -92,7 +92,8 @@ export class VideoFrameProcessor {
 			canvas.height = live?.source.height || wrapped.canvas.height;
 			decoder.canvas = canvas;
 			decoder.ctx = canvas.getContext("2d", { alpha: true }) ?? undefined;
-			decoder.texture = new pixi.Texture({ source: pixi.Texture.from(canvas).source, frame: live?.frame });
+			// A bare source: Texture.from would cache a texture per canvas that restore() never destroys.
+			decoder.texture = new pixi.Texture({ source: pixi.TextureSource.from(canvas), frame: live?.frame });
 		}
 
 		decoder.ctx?.drawImage(wrapped.canvas, 0, 0, decoder.canvas!.width, decoder.canvas!.height);
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index de6cadbd..e8d9c657 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -52,10 +52,8 @@ jest.mock("pixi.js", () => ({
 	// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports -- jest.mock factories can't use imports
 	...require("./helpers/pixi-mock-filters").pixiFilterStubs,
 	Rectangle: jest.fn().mockImplementation((x: number, y: number, width: number, height: number) => ({ x, y, width, height })),
-	Texture: Object.assign(
-		jest.fn((options: object) => ({ ...options, destroy: jest.fn() })),
-		{ from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
-	)
+	Texture: jest.fn((options: object) => ({ ...options, destroy: jest.fn() })),
+	TextureSource: { from: jest.fn(() => ({ update: jest.fn() })) }
 }));
 
 // The canvas package needs TextEncoder, which jsdom lacks; the export only uses its font-name parser.
diff --git a/tests/export-video-frames.test.ts b/tests/export-video-frames.test.ts
index 67750d25..fa8253ef 100644
--- a/tests/export-video-frames.test.ts
+++ b/tests/export-video-frames.test.ts
@@ -9,10 +9,8 @@ jest.mock("mediabunny", () => ({ Input: jest.fn(), UrlSource: jest.fn(), CanvasS
 jest.mock("pixi.js", () => ({
 	// eslint-disable-next-line global-require, @typescript-eslint/no-require-imports -- jest.mock factories can't use imports
 	...require("./helpers/pixi-mock-filters").pixiFilterStubs,
-	Texture: Object.assign(
-		jest.fn((options: object) => ({ ...options, destroy: jest.fn() })),
-		{ from: jest.fn(() => ({ source: { update: jest.fn() }, destroy: jest.fn() })) }
-	)
+	Texture: jest.fn((options: object) => ({ ...options, destroy: jest.fn() })),
+	TextureSource: { from: jest.fn(() => ({ update: jest.fn() })) }
 }));
 
 beforeAll(() => {

From 71c9a4e2fda65b00e401e0896d386a83c4203634 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:17:52 +1100
Subject: [PATCH 15/16] docs(export): say when playback stops a running export

---
 readme.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/readme.md b/readme.md
index a5382cb3..3566a20e 100644
--- a/readme.md
+++ b/readme.md
@@ -337,7 +337,7 @@ const exporter = new VideoExporter(edit, canvas);
 await exporter.export("my-video.mp4", 25);
 ```
 
-`exportBlob()` runs the same export without the progress overlay or the download and resolves with the MP4 `Blob`. `onProgress` receives a fraction from 0 to 1 and a stage label. Aborting the signal rejects with an `ExportError` whose `phase` is `cancelled`. The editor stays live while an export runs, but changing the edit, or playing, pausing or seeking, rejects the export with `phase` `export`.
+`exportBlob()` runs the same export without the progress overlay or the download and resolves with the MP4 `Blob`. `onProgress` receives a fraction from 0 to 1 and a stage label. Aborting the signal rejects with an `ExportError` whose `phase` is `cancelled`. The editor stays live while an export runs: changing the edit rejects the export with `phase` `export`, and so does playing, pausing or seeking once it has started drawing frames.
 
 ```typescript
 import { ExportError } from "@shotstack/shotstack-studio";

From ec9f35a11656f6a0637603654764634ac5c49436 Mon Sep 17 00:00:00 2001
From: dazzatronus <derkzomer@gmail.com>
Date: Mon, 19 Oct 2026 22:34:41 +1100
Subject: [PATCH 16/16] fix(export): keep cleanup paired when preparing a frame
 or starting an export throws

---
 src/core/export/export-coordinator.ts |  7 +++---
 tests/export-coordinator.test.ts      | 36 +++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/core/export/export-coordinator.ts b/src/core/export/export-coordinator.ts
index 996a0a8d..ca46cee2 100644
--- a/src/core/export/export-coordinator.ts
+++ b/src/core/export/export-coordinator.ts
@@ -109,20 +109,21 @@ export class ExportCoordinator {
 		throwIfAborted();
 		const report: Progress = (fraction, stage) => onProgress?.(fraction, stage);
 
-		exporting.add(this.edit);
 		let output: Output | undefined;
 		let changed = false;
 		const markChanged = (): void => {
 			changed = true;
 		};
-		const stopWatching = this.edit.events.on(EditEvent.EditChanged, markChanged);
+		let stopWatching = (): void => {};
 		// The editor stays live during export; anything checked, mixed or drawn before a change no longer matches the edit.
 		const throwIfStopped = (): void => {
 			throwIfAborted();
 			if (changed) throw new ExportError("The edit or playback changed during export", "export");
 		};
 
+		exporting.add(this.edit);
 		try {
+			stopWatching = this.edit.events.on(EditEvent.EditChanged, markChanged);
 			output = new Output({ format: new Mp4OutputFormat(), target: new BufferTarget() });
 			const cfg = this.prepareConfig(fps);
 			report(0, "Preparing...");
@@ -246,8 +247,8 @@ export class ExportCoordinator {
 
 				// update() only starts rich text and caption draws; finish this frame's before reading pixels.
 				const active = clips.filter(clip => clip.isActive());
-				await Promise.all(active.map(clip => clip.prepareStaticRender()));
 				try {
+					await Promise.all(active.map(clip => clip.prepareStaticRender()));
 					throwIfStopped();
 					// pixi renders the container into a texture with its own transform swapped for the frame's,
 					// so the editor's pan and zoom never reach these pixels; resolution pins them to output pixels.
diff --git a/tests/export-coordinator.test.ts b/tests/export-coordinator.test.ts
index e8d9c657..371c4a2e 100644
--- a/tests/export-coordinator.test.ts
+++ b/tests/export-coordinator.test.ts
@@ -513,6 +513,42 @@ describe("asynchronous drawing", () => {
 	});
 });
 
+describe("cleanup", () => {
+	it("ends every prepared draw when one fails, and rejects", async () => {
+		const { exporter, edit, renderer } = createHarness();
+		const clip = (prepare: () => Promise<void>) => ({
+			clipId: "title",
+			needsResolution: false,
+			update: jest.fn(),
+			isActive: () => true,
+			prepareStaticRender: jest.fn(prepare),
+			endStaticRender: jest.fn()
+		});
+		const drawn = clip(async () => {});
+		const failed = clip(async () => {
+			throw new Error("draw failed");
+		});
+		edit.tracks = [[drawn, failed]];
+
+		await expect(exporter.exportBlob()).rejects.toMatchObject({ phase: "export" });
+		expect(renderer.extract.pixels).not.toHaveBeenCalled();
+		expect(drawn.endStaticRender).toHaveBeenCalledTimes(1);
+		expect(failed.endStaticRender).toHaveBeenCalledTimes(1);
+		exporter.dispose();
+	});
+
+	it("releases the edit for the next export when watching it for changes fails", async () => {
+		const { exporter, edit } = createHarness();
+		jest.spyOn(edit.events, "on").mockImplementationOnce(() => {
+			throw new Error("listener limit");
+		});
+
+		await expect(exporter.exportBlob()).rejects.toMatchObject({ name: "ExportError", phase: "export" });
+		await expect(exporter.exportBlob()).resolves.toBeInstanceOf(Blob);
+		exporter.dispose();
+	});
+});
+
 describe("speed", () => {
 	it("decodes each video frame at the player's own source time for that frame", async () => {
 		const { exporter, edit } = createHarness();