Add InputTrack.number

docs/guide/converting-media-files.md

@@ -306,8 +306,8 @@ const conversion = await Conversion.init({
 	output,
 
 	// Function gets invoked for each video track:
-	video: (videoTrack, n) => {
-		if (n > 1) {
+	video: (videoTrack) => {
+		if (videoTrack.number > 1) {
 			// Keep only the first video track
 			return { discard: true };
 		}
@@ -319,7 +319,7 @@ const conversion = await Conversion.init({
 	},
 
 	// Async functions work too:
-	audio: async (audioTrack, n) => {
+	audio: async (audioTrack) => {
 		if (audioTrack.languageCode !== 'rus') {
 			// Keep only Russian audio tracks
 			return { discard: true };

docs/guide/quick-start.md

@@ -556,14 +556,16 @@ const output = new Output(...);
 const conversion = await Conversion.init({
 	input,
 	output,
-	video: {
+	video: track => ({
 		width: 480,
 		bitrate: QUALITY_LOW,
-	},
-	audio: {
+		discard: track.number > 1, // Keep only the first video track
+	}),
+	audio: track => ({
 		numberOfChannels: 1,
 		bitrate: QUALITY_LOW,
-	},
+		discard: track.number > 1, // Keep only the first audio track
+	}),
 	trim: {
 		// Let's keep only the first 60 seconds
 		start: 0,

docs/guide/reading-media-files.md

@@ -98,6 +98,10 @@ Once you have an `InputTrack`, you can start extracting metadata from it.
 // Get a unique ID for this track in the input file:
 track.id; // => number
 
+// Get the 1-based index of this track among all tracks of the same type
+// (e.g., first video track is 1, second video track is 2, etc.):
+track.number; // => number
+
 // Check the track's type:
 track.type; // => 'video' | 'audio' | 'subtitle';
 

examples/file-compression/file-compression.ts

@@ -62,13 +62,15 @@ const compressFile = async (resource: File | string) => {
 		currentConversion = await Conversion.init({
 			input,
 			output,
-			video: {
+			video: track => ({
 				width: 320, // Height will be deduced automatically to retain aspect ratio
 				bitrate: QUALITY_VERY_LOW,
-			},
-			audio: {
+				discard: track.number > 1, // Keep only the first video track
+			}),
+			audio: track => ({
 				bitrate: 32e3,
-			},
+				discard: track.number > 1, // Keep only the first audio track
+			}),
 		});
 
 		// Keep track of progress

src/adts/adts-demuxer.ts

@@ -146,6 +146,10 @@ class AdtsAudioTrackBacking implements InputAudioTrackBacking {
 		return 1;
 	}
 
+	getNumber() {
+		return 1;
+	}
+
 	async getFirstTimestamp() {
 		return 0;
 	}

src/conversion.ts

@@ -66,7 +66,8 @@ export type ConversionOptions = {
 	 * Video-specific options. When passing an object, the same options are applied to all video tracks. When passing a
 	 * function, it will be invoked for each video track and is expected to return or resolve to the options
 	 * for that specific track. The function is passed an instance of {@link InputVideoTrack} as well as a number `n`,
-	 * which is the 1-based index of the track in the list of all video tracks.
+	 * which is the 1-based index of the track in the list of all video tracks. Using `n` is deprecated, prefer the
+	 * identical `track.number` instead.
 	 */
 	video?: ConversionVideoOptions
 		| ((track: InputVideoTrack, n: number) => MaybePromise<ConversionVideoOptions | undefined>);
@@ -75,7 +76,8 @@ export type ConversionOptions = {
 	 * Audio-specific options. When passing an object, the same options are applied to all audio tracks. When passing a
 	 * function, it will be invoked for each audio track and is expected to return or resolve to the options
 	 * for that specific track. The function is passed an instance of {@link InputAudioTrack} as well as a number `n`,
-	 * which is the 1-based index of the track in the list of all audio tracks.
+	 * which is the 1-based index of the track in the list of all audio tracks. Using `n` is deprecated, prefer the
+	 * identical `track.number` instead.
 	 */
 	audio?: ConversionAudioOptions
 		| ((track: InputAudioTrack, n: number) => MaybePromise<ConversionAudioOptions | undefined>);

src/flac/flac-demuxer.ts

@@ -529,6 +529,10 @@ class FlacAudioTrackBacking implements InputAudioTrackBacking {
 		return 1;
 	}
 
+	getNumber() {
+		return 1;
+	}
+
 	getCodec() {
 		return 'flac' as const;
 	}

src/input-track.ts

@@ -32,6 +32,7 @@ export type PacketStats = {
 
 export interface InputTrackBacking {
 	getId(): number;
+	getNumber(): number;
 	getCodec(): MediaCodec | null;
 	getInternalCodecId(): string | number | Uint8Array | null;
 	getName(): string | null;
@@ -94,6 +95,15 @@ export abstract class InputTrack {
 		return this._backing.getId();
 	}
 
+	/**
+	 * The 1-based index of this track among all tracks of the same type in the input file. For example, the first
+	 * video track has number 1, the second video track has number 2, and so on. The index refers to the order in
+	 * which the tracks are returned by {@link Input.getTracks()}.
+	 */
+	get number() {
+		return this._backing.getNumber();
+	}
+
 	/**
 	 * The identifier of the codec used internally by the container. It is not homogenized by Mediabunny
 	 * and depends entirely on the container format.

src/isobmff/isobmff-demuxer.ts

@@ -2335,6 +2335,25 @@ abstract class IsobmffTrackBacking implements InputTrackBacking {
 		return this.internalTrack.id;
 	}
 
+	getNumber() {
+		const demuxer = this.internalTrack.demuxer;
+		const inputTrack = this.internalTrack.inputTrack!;
+		const trackType = inputTrack.type;
+
+		let number = 0;
+		for (const track of demuxer.tracks) {
+			if (track.inputTrack!.type === trackType) {
+				number++;
+			}
+
+			if (track === this.internalTrack) {
+				break;
+			}
+		}
+
+		return number;
+	}
+
 	getCodec(): MediaCodec | null {
 		throw new Error('Not implemented on base class.');
 	}

src/matroska/matroska-demuxer.ts

@@ -1859,6 +1859,27 @@ abstract class MatroskaTrackBacking implements InputTrackBacking {
 		return this.internalTrack.id;
 	}
 
+	getNumber() {
+		const demuxer = this.internalTrack.demuxer;
+		const inputTrack = this.internalTrack.inputTrack!;
+		const trackType = inputTrack.type;
+
+		let number = 0;
+		for (const segment of demuxer.segments) {
+			for (const track of segment.tracks) {
+				if (track.inputTrack!.type === trackType) {
+					number++;
+				}
+
+				if (track === this.internalTrack) {
+					break;
+				}
+			}
+		}
+
+		return number;
+	}
+
 	getCodec(): MediaCodec | null {
 		throw new Error('Not implemented on base class.');
 	}

src/mp3/mp3-demuxer.ts

@@ -217,6 +217,10 @@ class Mp3AudioTrackBacking implements InputAudioTrackBacking {
 		return 1;
 	}
 
+	getNumber() {
+		return 1;
+	}
+
 	async getFirstTimestamp() {
 		return 0;
 	}

src/mpeg-ts/mpeg-ts-demuxer.ts

@@ -746,6 +746,25 @@ export abstract class MpegTsTrackBacking implements InputTrackBacking {
 		return this.elementaryStream.pid;
 	}
 
+	getNumber() {
+		const demuxer = this.elementaryStream.demuxer;
+		const trackType = this.elementaryStream.info.type;
+
+		let number = 0;
+		for (const track of demuxer.tracks) {
+			if (track.type === trackType) {
+				number++;
+			}
+
+			assert(track._backing instanceof MpegTsTrackBacking);
+			if (track._backing.elementaryStream === this.elementaryStream) {
+				break;
+			}
+		}
+
+		return number;
+	}
+
 	getCodec(): MediaCodec | null {
 		throw new Error('Not implemented on base class.');
 	}

src/ogg/ogg-demuxer.ts

@@ -428,6 +428,16 @@ class OggAudioTrackBacking implements InputAudioTrackBacking {
 		return this.bitstream.serialNumber;
 	}
 
+	getNumber() {
+		// All Ogg tracks are audio, so the track's index + 1 is its number
+		const index = this.demuxer.tracks.findIndex(
+			t => (t._backing as OggAudioTrackBacking).bitstream === this.bitstream,
+		);
+		assert(index !== -1);
+
+		return index + 1;
+	}
+
 	getNumberOfChannels() {
 		return this.bitstream.numberOfChannels;
 	}

src/wave/wave-demuxer.ts

@@ -356,6 +356,10 @@ class WaveAudioTrackBacking implements InputAudioTrackBacking {
 		return 1;
 	}
 
+	getNumber() {
+		return 1;
+	}
+
 	getCodec() {
 		return this.demuxer.getCodec();
 	}