Sanitize initial HEVC packet to avoid Chromium's validation logic from tripping up (#314)

dev/demux.html

@@ -11,23 +11,22 @@
 	document.body.append(fileInput);
 
 	fileInput.addEventListener('change', async () => {
-		/*
 		const file = fileInput.files[0];
 		const input = new Mediabunny.Input({
 			formats: Mediabunny.ALL_FORMATS,
 			source: new Mediabunny.BlobSource(file),
 		});
 
-		const track = await input.getPrimaryAudioTrack();
-		const sink3 = new Mediabunny.EncodedPacketSink(track);
-		console.log((await sink3.getFirstPacket()).data.join(', '));
-		return;
-		console.log(await track.getDurationFromMetadata(), await track.computeDuration());
+		const track = await input.getPrimaryVideoTrack();
+		const sink = new Mediabunny.EncodedPacketSink(track);
+		const packet = await sink.getFirstKeyPacket();
 
-		//console.log(await input.getDurationFromMetadata(), await input.computeDuration());
-		return;
-		*/
+		console.log(packet.data.join(', '));
 
+		const config = await track.getDecoderConfig();
+		console.log(config.description.join(', '));
+
+		/*
 		const input = new Mediabunny.Input({
 			source: new Mediabunny.UrlSource('https://storage.googleapis.com/shaka-demo-assets/angel-one-widevine-hls/hls.m3u8'),
 			formats: Mediabunny.ALL_FORMATS,
@@ -36,6 +35,7 @@
 		const videoTrack = await input.getPrimaryVideoTrack();
 		const sink = new Mediabunny.EncodedPacketSink(videoTrack);
 		console.log(await sink.getFirstPacket());
+		*/
 
 		/*
 		return

src/codec-data.ts

@@ -866,6 +866,21 @@ export type HevcSpsInfo = {
 	minSpatialSegmentationIdc: number;
 };
 
+export const concatHevcNalUnits = (nalUnits: Uint8Array[], decoderConfig: VideoDecoderConfig) => {
+	if (decoderConfig.description) {
+		// Stream is length-prefixed. Let's extract the size of the length prefix from the decoder config
+
+		const bytes = toUint8Array(decoderConfig.description);
+		const lengthSizeMinusOne = bytes[21]! & 0b11;
+		const lengthSize = (lengthSizeMinusOne + 1) as 1 | 2 | 3 | 4;
+
+		return concatNalUnitsInLengthPrefixed(nalUnits, lengthSize);
+	} else {
+		// Stream is in Annex B format
+		return concatNalUnitsInAnnexB(nalUnits);
+	}
+};
+
 export const iterateHevcNalUnits = (packetData: Uint8Array, decoderConfig: VideoDecoderConfig) => {
 	if (decoderConfig.description) {
 		const bytes = toUint8Array(decoderConfig.description);
@@ -1602,6 +1617,103 @@ export const deserializeHevcDecoderConfigurationRecord = (data: Uint8Array): Hev
 	}
 };
 
+enum HevcNaluOrderState {
+	audAllowed,
+	beforeFirstVcl,
+	afterFirstVcl,
+	eoBitstreamAllowed,
+	noMoreDataAllowed,
+}
+
+// This function sanitzes the contents of an HEVC packet such that
+// https://source.chromium.org/chromium/chromium/src/+/main:media/formats/mp4/hevc.cc's validation logic does not trip
+// up on its contents. The validation is often too strict and rejects packets that Chromium could decode just fine.
+// Chromium code retrieved on 2026-04-29.
+// See https://issues.chromium.org/issues/507611247.
+export const sanitizeHevcPacketForChromium = (
+	packetData: Uint8Array,
+	decoderConfig: VideoDecoderConfig,
+): Uint8Array | null => {
+	const removedNalUnits = new Set<number>();
+	let orderState: HevcNaluOrderState = HevcNaluOrderState.audAllowed;
+
+	for (const loc of iterateHevcNalUnits(packetData, decoderConfig)) {
+		if (orderState === HevcNaluOrderState.noMoreDataAllowed) {
+			removedNalUnits.add(loc.offset);
+			continue;
+		}
+
+		const type = extractNalUnitTypeForHevc(packetData[loc.offset]!);
+
+		if (orderState === HevcNaluOrderState.eoBitstreamAllowed && type !== 37 /* EOB_NUT */) {
+			removedNalUnits.add(loc.offset);
+			continue;
+		}
+
+		let remove = false;
+
+		if (type === 35) { // AUD_NUT
+			if (orderState > HevcNaluOrderState.audAllowed) {
+				remove = true;
+			} else {
+				orderState = HevcNaluOrderState.beforeFirstVcl;
+			}
+		} else if (type <= 31) { // VCL (0-31)
+			if (orderState > HevcNaluOrderState.afterFirstVcl) {
+				remove = true;
+			} else {
+				orderState = HevcNaluOrderState.afterFirstVcl;
+			}
+		} else if (type === 36) { // EOS_NUT
+			if (orderState !== HevcNaluOrderState.afterFirstVcl) {
+				remove = true;
+			} else {
+				orderState = HevcNaluOrderState.eoBitstreamAllowed;
+			}
+		} else if (type === 37) { // EOB_NUT
+			if (orderState < HevcNaluOrderState.afterFirstVcl) {
+				remove = true;
+			} else {
+				orderState = HevcNaluOrderState.noMoreDataAllowed;
+			}
+		} else if (
+			type === 32 || type === 33 || type === 34 || type === 39
+			|| (type >= 41 && type <= 44) || (type >= 48 && type <= 55)
+		) { // VPS, SPS, PPS, PREFIX_SEI, RSV_NVCL41..44, UNSPEC48..55
+			if (orderState > HevcNaluOrderState.beforeFirstVcl) {
+				remove = true;
+			} else {
+				orderState = HevcNaluOrderState.beforeFirstVcl;
+			}
+		} else if (
+			type === 38 || type === 40
+			|| (type >= 45 && type <= 47) || (type >= 56 && type <= 63)
+		) { // FD, SUFFIX_SEI, RSV_NVCL45..47, UNSPEC56..63
+			if (orderState < HevcNaluOrderState.afterFirstVcl) {
+				remove = true;
+			}
+		}
+
+		if (remove) {
+			removedNalUnits.add(loc.offset);
+		}
+	}
+
+	// If nothing violated the rules, return null to signal that
+	if (removedNalUnits.size === 0) {
+		return null;
+	}
+
+	const filteredNalUnits: Uint8Array[] = [];
+	for (const loc of iterateHevcNalUnits(packetData, decoderConfig)) {
+		if (!removedNalUnits.has(loc.offset)) {
+			filteredNalUnits.push(packetData.subarray(loc.offset, loc.offset + loc.length));
+		}
+	}
+
+	return concatHevcNalUnits(filteredNalUnits, decoderConfig);
+};
+
 export type Vp9CodecInfo = {
 	profile: number;
 	level: number;

src/media-sink.ts

@@ -17,6 +17,7 @@ import {
 	iterateAvcNalUnits,
 	iterateHevcNalUnits,
 	parseAvcSps,
+	sanitizeHevcPacketForChromium,
 } from './codec-data';
 import { CustomVideoDecoder, customVideoDecoders, CustomAudioDecoder, customAudioDecoders } from './custom-coder';
 import { InputDisposedError } from './input';
@@ -980,8 +981,9 @@ class VideoDecoderWrapper extends DecoderWrapper<VideoSample> {
 				insertSorted(this.inputTimestamps, packet.timestamp, x => x);
 			}
 
+			if (isChromium() && this.currentPacketIndex === 0) {
+				if (this.codec === 'avc') {
 					// Workaround for https://issues.chromium.org/issues/470109459
-			if (isChromium() && this.currentPacketIndex === 0 && this.codec === 'avc') {
 					const filteredNalUnits: Uint8Array[] = [];
 
 					for (const loc of iterateAvcNalUnits(packet.data, this.decoderConfig)) {
@@ -994,6 +996,13 @@ class VideoDecoderWrapper extends DecoderWrapper<VideoSample> {
 
 					const newData = concatAvcNalUnits(filteredNalUnits, this.decoderConfig);
 					packet = new EncodedPacket(newData, packet.type, packet.timestamp, packet.duration);
+				} else if (this.codec === 'hevc') {
+					// Workaround for https://issues.chromium.org/issues/507611247
+					const sanitizedData = sanitizeHevcPacketForChromium(packet.data, this.decoderConfig);
+					if (sanitizedData) {
+						packet = new EncodedPacket(sanitizedData, packet.type, packet.timestamp, packet.duration);
+					}
+				}
 			}
 
 			this.decoder.decode(packet.toEncodedVideoChunk());