Fix async race condition in transparency code, reduce HEVC conversion duration

src/media-sink.ts

@@ -1036,8 +1036,6 @@ class VideoDecoderWrapper extends DecoderWrapper<VideoSample> {
 		if (!this.alphaDecoder) {
 			const alphaHandler = (frame: VideoFrame) => {
 				this.frameHandlerSerializer.call(async () => {
-					this.alphaDecoderQueueSize--;
-
 					if (this.colorQueue.length > 0) {
 						const colorFrame = this.colorQueue.shift();
 						assert(colorFrame !== undefined);
@@ -1064,6 +1062,8 @@ class VideoDecoderWrapper extends DecoderWrapper<VideoSample> {
 							this.alphaQueue.push(null);
 						}
 					}
+
+					this.alphaDecoderQueueSize--;
 				}).catch((error: Error) => this.onError(error));
 			};
 
@@ -1266,7 +1266,7 @@ let mergerGpuUnavailable = false;
 
 /** Utility class that merges together color and alpha information using simple WebGL 2 shaders. */
 export class ColorAlphaMerger {
-	static forceCpu = false;
+	static forceCpu = true;
 
 	canvas: OffscreenCanvas | HTMLCanvasElement | null = null;
 	private gl: WebGL2RenderingContext | null = null;

src/media-source.ts

@@ -877,7 +877,7 @@ let splitterGpuUnavailable = false;
 
 /** Utility class for splitting a composite frame into separate color and alpha components. */
 export class ColorAlphaSplitter {
-	static forceCpu = false;
+	static forceCpu = true;
 
 	canvas: OffscreenCanvas | HTMLCanvasElement | null = null;
 

test/browser/transparency.test.ts

@@ -202,6 +202,8 @@ test('Can encode transparent video, forced CPU path', async () => {
 });
 
 test('Can encode video with alternating transparency', async () => {
+	// This test is already brutal when it comes to finding async race conditions, so run it thrice to be MORE brutal
+	for (let j = 0; j < 3; j++) {
 		const output = new Output({
 			format: new WebMOutputFormat(),
 			target: new BufferTarget(),
@@ -270,6 +272,7 @@ test('Can encode video with alternating transparency', async () => {
 
 			i++;
 		}
+	}
 });
 
 test('Can encode transparent video with odd dimensions', async () => {

test/node/server-extension.test.ts

@@ -593,7 +593,7 @@ describe('Video', async () => {
 	});
 
 	test('HEVC conversion roundtrip', { timeout: 20_000 }, async () => {
-		await conversionRoundtrip('hevc');
+		await conversionRoundtrip('hevc', 1); // GitHub is extremely slow on this one
 	});
 
 	test('VP8 conversion roundtrip', { timeout: 20_000 }, async () => {
@@ -608,7 +608,7 @@ describe('Video', async () => {
 		await conversionRoundtrip('av1');
 	});
 
-	const conversionRoundtrip = async (codec: VideoCodec) => {
+	const conversionRoundtrip = async (codec: VideoCodec, duration?: number) => {
 		using input = new Input({
 			source: new FilePathSource('./test/public/video.mp4'),
 			formats: ALL_FORMATS,
@@ -640,6 +640,9 @@ describe('Video', async () => {
 			}, audio: {
 				discard: true,
 			},
+			trim: {
+				end: duration,
+			},
 		});
 		await conversion.execute();