Add fan-out API to Conversion API, fix erroneous track count validation

test/browser/conversion.test.ts

@@ -1,12 +1,13 @@
 import { ALL_FORMATS } from '../../src/input-format.js';
 import { Input } from '../../src/input.js';
-import { Mp4OutputFormat } from '../../src/output-format.js';
+import { AdtsOutputFormat, Mp4OutputFormat } from '../../src/output-format.js';
 import { Output } from '../../src/output.js';
 import { BufferSource, UrlSource } from '../../src/source.js';
 import { expect, test } from 'vitest';
 import { BufferTarget } from '../../src/target.js';
 import { Conversion } from '../../src/conversion.js';
 import { assert } from '../../src/misc.js';
+import { InputVideoTrack } from '../../src/input-track.js';
 
 test('Rotation is baked-in when rerendering', async () => {
 	using input = new Input({
@@ -47,3 +48,55 @@ test('Rotation is baked-in when rerendering', async () => {
 	expect(await track.getDisplayHeight()).toBe(570);
 	expect(await track.getRotation()).toBe(0);
 });
+
+test('Exceeding max allowed track count', async () => {
+	using input = new Input({
+		source: new UrlSource('/multiple-aac-tracks.mp4'),
+		formats: ALL_FORMATS,
+	});
+
+	const output = new Output({
+		format: new AdtsOutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const conversion = await Conversion.init({ input, output });
+	expect(conversion.utilizedTracks).toHaveLength(1);
+	expect(conversion.discardedTracks).toHaveLength(1);
+	expect(conversion.discardedTracks[0]!.reason).toBe('max_track_count_reached');
+});
+
+test.only('Fan-out', async () => {
+	using input = new Input({
+		source: new UrlSource('/video.mp4'),
+		formats: ALL_FORMATS,
+	});
+
+	const output = new Output({
+		format: new Mp4OutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const conversion = await Conversion.init({
+		input,
+		output,
+		video: [{ height: 480 }, { height: 360 }],
+		audio: [], // Identical to discarding it
+	});
+	expect(conversion.utilizedTracks).toHaveLength(2);
+	expect(conversion.discardedTracks).toHaveLength(1);
+	expect(conversion.discardedTracks[0]!.reason).toBe('discarded_by_user');
+
+	await conversion.execute();
+
+	using otherInput = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+
+	const tracks = await otherInput.getTracks() as InputVideoTrack[];
+	expect(tracks.map(x => x.type)).toEqual(['video', 'video']);
+
+	expect(await tracks[0]!.getDisplayHeight()).toBe(480);
+	expect(await tracks[1]!.getDisplayHeight()).toBe(360);
+});