Add track name support

src/matroska/ebml.ts

@@ -7,13 +7,22 @@
  */
 
 import { MediaCodec } from '../codec';
+import { assertNever, textDecoder, textEncoder } from '../misc';
 import { Reader } from '../reader';
 import { Writer } from '../writer';
 
 export interface EBMLElement {
 	id: number;
 	size?: number;
-	data: number | string | Uint8Array | EBMLFloat32 | EBMLFloat64 | EBMLSignedInt | (EBML | null)[];
+	data:
+		| number
+		| string
+		| Uint8Array
+		| EBMLFloat32
+		| EBMLFloat64
+		| EBMLSignedInt
+		| EBMLUnicodeString
+		| (EBML | null)[];
 }
 
 export type EBML = EBMLElement | Uint8Array | (EBML | null)[];
@@ -45,6 +54,10 @@ export class EBMLSignedInt {
 	}
 }
 
+export class EBMLUnicodeString {
+	constructor(public value: string) {}
+}
+
 /** Defines some of the EBML IDs used by Matroska files. */
 export enum EBMLId {
 	EBML = 0x1a45dfa3,
@@ -73,6 +86,7 @@ export enum EBMLId {
 	FlagDefault = 0x88,
 	FlagForced = 0x55aa,
 	FlagLacing = 0x9c,
+	Name = 0x536e,
 	Language = 0x22b59c,
 	CodecID = 0x86,
 	CodecPrivate = 0x63a2,
@@ -371,6 +385,12 @@ export class EBMLWriter {
 				const size = data.size ?? measureSignedInt(data.data.value);
 				this.writeVarInt(size);
 				this.writeSignedInt(data.data.value, size);
+			} else if (data.data instanceof EBMLUnicodeString) {
+				const bytes = textEncoder.encode(data.data.value);
+				this.writeVarInt(bytes.length);
+				this.writer.write(bytes);
+			} else {
+				assertNever(data.data);
 			}
 		}
 	}
@@ -514,6 +534,19 @@ export class EBMLReader {
 		return String.fromCharCode(...new Uint8Array(view.buffer, offset, strLength));
 	}
 
+	readUnicodeString(length: number) {
+		const { view, offset } = this.reader.getViewAndOffset(this.pos, this.pos + length);
+		this.pos += length;
+
+		// Actual string length might be shorter due to null terminators
+		let strLength = 0;
+		while (strLength < length && view.getUint8(offset + strLength) !== 0) {
+			strLength += 1;
+		}
+
+		return textDecoder.decode(new Uint8Array(view.buffer, offset, strLength));
+	}
+
 	readElementId() {
 		const size = this.readVarIntSize();
 		if (size === null) {

src/matroska/matroska-demuxer.ts

@@ -145,6 +145,7 @@ type InternalTrack = {
 	codecId: string | null;
 	codecPrivate: Uint8Array | null;
 	defaultDuration: number | null;
+	name: string | null;
 	languageCode: string;
 	info:
 		| null
@@ -836,6 +837,7 @@ export class MatroskaDemuxer extends Demuxer {
 					codecId: null,
 					codecPrivate: null,
 					defaultDuration: null,
+					name: null,
 					languageCode: UNDETERMINED_LANGUAGE,
 					info: null,
 				};
@@ -1004,6 +1006,12 @@ export class MatroskaDemuxer extends Demuxer {
 					= this.currentTrack.segment.timestampFactor * reader.readUnsignedInt(size) / 1e9;
 			}; break;
 
+			case EBMLId.Name: {
+				if (!this.currentTrack) break;
+
+				this.currentTrack.name = reader.readUnicodeString(size);
+			}; break;
+
 			case EBMLId.Language: {
 				if (!this.currentTrack) break;
 
@@ -1261,6 +1269,10 @@ abstract class MatroskaTrackBacking implements InputTrackBacking {
 		return (lastPacket?.timestamp ?? 0) + (lastPacket?.duration ?? 0);
 	}
 
+	getName() {
+		return this.internalTrack.name;
+	}
+
 	getLanguageCode() {
 		return this.internalTrack.languageCode;
 	}

src/matroska/matroska-muxer.ts

@@ -29,6 +29,7 @@ import {
 	EBMLFloat64,
 	EBMLId,
 	EBMLSignedInt,
+	EBMLUnicodeString,
 	EBMLWriter,
 } from './ebml';
 import { buildMatroskaMimeType } from './matroska-misc';
@@ -272,6 +273,9 @@ export class MatroskaMuxer extends Muxer {
 				{ id: EBMLId.CodecID, data: codecId },
 				{ id: EBMLId.CodecDelay, data: 0 },
 				{ id: EBMLId.SeekPreRoll, data: seekPreRollNs },
+				trackData.track.metadata.name !== undefined
+					? { id: EBMLId.Name, data: new EBMLUnicodeString(trackData.track.metadata.name) }
+					: null,
 				(trackData.type === 'video' ? this.videoSpecificTrackInfo(trackData) : null),
 				(trackData.type === 'audio' ? this.audioSpecificTrackInfo(trackData) : null),
 				(trackData.type === 'subtitle' ? this.subtitleSpecificTrackInfo(trackData) : null),