Add maxLiveSegmentCount HLS option

src/hls/hls-muxer.ts

@@ -61,6 +61,7 @@ type Playlist = {
 	writtenSegments: PlaylistSegment[];
 	peakBitrate: number | null;
 	averageBitrate: number | null;
+	mediaSequence: number;
 	done: boolean;
 
 	singleFile: {
@@ -88,6 +89,7 @@ export class HlsMuxer extends Muxer {
 	trackDatas: HlsTrackData[] = [];
 	singleFilePerPlaylist: boolean;
 	isLive: boolean;
+	maxLiveSegmentCount: number;
 	isRelativeToUnixEpoch = false;
 	globalTargetDuration: number;
 
@@ -105,6 +107,7 @@ export class HlsMuxer extends Muxer {
 		this.targetSegmentDuration = format._options.targetDuration ?? 2;
 		this.singleFilePerPlaylist = format._options.singleFilePerPlaylist ?? false;
 		this.isLive = format._options.live ?? false;
+		this.maxLiveSegmentCount = format._options.maxLiveSegmentCount ?? Infinity;
 		this.globalTargetDuration = this.targetSegmentDuration;
 
 		this.getPlaylistPath = format._options.getPlaylistPath
@@ -440,6 +443,7 @@ export class HlsMuxer extends Muxer {
 				writtenSegments: [],
 				peakBitrate: null,
 				averageBitrate: null,
+				mediaSequence: 0,
 				done: false,
 				singleFile: null,
 			};
@@ -1024,6 +1028,11 @@ export class HlsMuxer extends Muxer {
 			}
 
 			if (this.isLive) {
+				while (playlist.writtenSegments.length > this.maxLiveSegmentCount) {
+					playlist.writtenSegments.shift();
+					playlist.mediaSequence++;
+				}
+
 				await this.writePlaylist(playlist);
 				await this.tryWriteMasterPlaylist();
 			}
@@ -1128,6 +1137,7 @@ export class HlsMuxer extends Muxer {
 			+ `#EXT-X-VERSION:${version}\n`
 			+ (!this.isLive ? '#EXT-X-PLAYLIST-TYPE:VOD\n' : '')
 			+ `#EXT-X-TARGETDURATION:${Math.ceil(targetDuration)}\n` // Must be a "decimal-integer"
+			+ (Number.isFinite(this.maxLiveSegmentCount) ? `#EXT-X-MEDIA-SEQUENCE:${playlist.mediaSequence}\n` : '')
 			+ '#EXT-X-INDEPENDENT-SEGMENTS\n' // Todo not for live?
 			+ (isKeyPacketsOnly ? '#EXT-X-I-FRAMES-ONLY\n' : '')
 			+ (playlist.initSegment

src/output-format.ts

@@ -1173,6 +1173,7 @@ export type HlsOutputFormatOptions = {
 	targetDuration?: number;
 	singleFilePerPlaylist?: boolean;
 	live?: boolean;
+	maxLiveSegmentCount?: number;
 	getPlaylistPath?: (info: HlsOutputPlaylistInfo) => MaybePromise<string>;
 	getSegmentPath?: (info: HlsOutputSegmentInfo) => MaybePromise<string>;
 	getInitPath?: (info: HlsOutputPlaylistInfo) => MaybePromise<string>;
@@ -1217,6 +1218,13 @@ export class HlsOutputFormat extends OutputFormat {
 		if (options.live !== undefined && typeof options.live !== 'boolean') {
 			throw new TypeError('options.live, when provided, must be a boolean.');
 		}
+		if (
+			options.maxLiveSegmentCount !== undefined
+			&& (typeof options.maxLiveSegmentCount !== 'number' || options.maxLiveSegmentCount < 1
+				|| (Number.isFinite(options.maxLiveSegmentCount) && !Number.isInteger(options.maxLiveSegmentCount)))
+		) {
+			throw new TypeError('options.maxLiveSegmentCount, when provided, must be a positive integer or Infinity.');
+		}
 		if (options.getPlaylistPath !== undefined && typeof options.getPlaylistPath !== 'function') {
 			throw new TypeError('options.getPlaylistPath, when provided, must be a function.');
 		}

test/node/hls-output.test.ts

@@ -2523,3 +2523,103 @@ test('Throws if some tracks are relativeToUnixEpoch and some are not', async ()
 
 	await expect(output.start()).rejects.toThrow('relativeToUnixEpoch');
 });
+
+test('Live mode, maxLiveSegmentCount', async () => {
+	const writtenTexts = new Map<string, string>();
+
+	const output = new Output({
+		format: new HlsOutputFormat({
+			segmentFormat: new MpegTsOutputFormat(),
+			live: true,
+			maxLiveSegmentCount: 2,
+		}),
+		target: (request) => {
+			const target = new BufferTarget();
+			target.on('finalized', () => {
+				if (request.path.endsWith('.m3u8')) {
+					writtenTexts.set(request.path, new TextDecoder().decode(target.buffer!));
+				}
+			});
+			return target;
+		},
+		rootPath: 'master.m3u8',
+	});
+
+	const source = videoSource();
+	output.addVideoTrack(source);
+
+	await output.start();
+
+	await source.add(new EncodedPacket(avcPacketData, 'key', 0, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 0.5, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 1, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 1.5, 0.5), avcMetadata);
+
+	await source.add(new EncodedPacket(avcPacketData, 'key', 2, 0.5), avcMetadata);
+
+	expect(writtenTexts.get('playlist-1.m3u8')).toBe(`#EXTM3U
+#EXT-X-VERSION:3
+#EXT-X-TARGETDURATION:2
+#EXT-X-MEDIA-SEQUENCE:0
+#EXT-X-INDEPENDENT-SEGMENTS
+
+#EXTINF:2,
+segment-1-1.ts
+`);
+
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 2.5, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 3, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 3.5, 0.5), avcMetadata);
+
+	await source.add(new EncodedPacket(avcPacketData, 'key', 4, 0.5), avcMetadata);
+
+	expect(writtenTexts.get('playlist-1.m3u8')).toBe(`#EXTM3U
+#EXT-X-VERSION:3
+#EXT-X-TARGETDURATION:2
+#EXT-X-MEDIA-SEQUENCE:0
+#EXT-X-INDEPENDENT-SEGMENTS
+
+#EXTINF:2,
+segment-1-1.ts
+#EXTINF:2,
+segment-1-2.ts
+`);
+
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 4.5, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 5, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 5.5, 0.5), avcMetadata);
+
+	await source.add(new EncodedPacket(avcPacketData, 'key', 6, 0.5), avcMetadata);
+
+	expect(writtenTexts.get('playlist-1.m3u8')).toBe(`#EXTM3U
+#EXT-X-VERSION:3
+#EXT-X-TARGETDURATION:2
+#EXT-X-MEDIA-SEQUENCE:1
+#EXT-X-INDEPENDENT-SEGMENTS
+
+#EXTINF:2,
+segment-1-2.ts
+#EXTINF:2,
+segment-1-3.ts
+`);
+
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 6.5, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 7, 0.5), avcMetadata);
+	await source.add(new EncodedPacket(avcPacketData, 'delta', 7.5, 0.5), avcMetadata);
+
+	await output.finalize();
+
+	expect(writtenTexts.get('playlist-1.m3u8')).toBe(`#EXTM3U
+#EXT-X-VERSION:3
+#EXT-X-TARGETDURATION:2
+#EXT-X-MEDIA-SEQUENCE:2
+#EXT-X-INDEPENDENT-SEGMENTS
+
+#EXTINF:2,
+segment-1-3.ts
+#EXTINF:2,
+segment-1-4.ts
+
+#EXT-X-ENDLIST
+`);
+});