feat(HLS): Add support for EXT-X-START (#6938)

Author: avelad

externs/shaka/manifest.js

@@ -25,7 +25,8 @@
  *   nextUrl: ?string,
  *   periodCount: number,
  *   gapCount: number,
- *   isLowLatency: boolean
+ *   isLowLatency: boolean,
+ *   startTime: ?number
  * }}
  *
  * @description
@@ -111,6 +112,10 @@
  *   If in src= mode or nothing is loaded, NaN.
  * @property {bolean} isLowLatency
  *   If true, the manifest is Low Latency.
+ * @property {?number} startTime
+ *   Indicate the startTime of the playback, when <code>startTime</code> is
+ *   <code>null</code>, playback will start at the default start time.
+ *   Note: It only overrides the load startTime when it is not defined.
  *
  * @exportDoc
  */

lib/dash/dash_parser.js

@@ -790,6 +790,7 @@ shaka.dash.DashParser = class {
         periodCount: periods.length,
         gapCount: this.gapCount_,
         isLowLatency: this.isLowLatency_,
+        startTime: null,
       };
 
       // We only need to do clock sync when we're using presentation start

lib/hls/hls_parser.js

@@ -267,6 +267,9 @@ shaka.hls.HlsParser = class {
 
     /** @private {HTMLMediaElement} */
     this.mediaElement_ = null;
+
+    /** @private {?number} */
+    this.startTime_ = null;
   }
 
 
@@ -937,6 +940,8 @@ shaka.hls.HlsParser = class {
           shaka.util.Error.Code.OPERATION_ABORTED);
     }
 
+    this.determineStartTime_(playlist);
+
     // Single-variant streams aren't lazy-loaded, so for them we already have
     // enough info here to determine the presentation type and duration.
     if (playlist.type == shaka.hls.PlaylistType.MEDIA) {
@@ -971,6 +976,7 @@ shaka.hls.HlsParser = class {
       periodCount: 1,
       gapCount: 0,
       isLowLatency: false,
+      startTime: this.startTime_,
     };
 
     // If there is no 'CODECS' attribute in the manifest and codec guessing is
@@ -2450,6 +2456,8 @@ shaka.hls.HlsParser = class {
 
       const realStream = realStreamInfo.stream;
 
+      this.determineStartTime_(playlist);
+
       if (this.isLive_() && !wasLive) {
         // Now that we know that the presentation is live, convert the timeline
         // to live.
@@ -2564,6 +2572,10 @@ shaka.hls.HlsParser = class {
 
       this.processDateRangeTags_(
           playlist.tags, stream.type, mediaVariables, getUris);
+
+      if (this.manifest_) {
+        this.manifest_.startTime = this.startTime_;
+      }
     };
 
     /** @type {Promise} */
@@ -3201,6 +3213,24 @@ shaka.hls.HlsParser = class {
   }
 
 
+  /**
+   * @param {!shaka.hls.Playlist} playlist
+   * @private
+   */
+  determineStartTime_(playlist) {
+    // If we already have a starttime we avoid processing this again.
+    if (this.startTime_ != null) {
+      return;
+    }
+    const startTimeTag =
+        shaka.hls.Utils.getFirstTagWithName(playlist.tags, 'EXT-X-START');
+    if (startTimeTag) {
+      this.startTime_ =
+          Number(startTimeTag.getRequiredAttrValue('TIME-OFFSET'));
+    }
+  }
+
+
   /**
    * @param {!shaka.hls.Playlist} playlist
    * @private
@@ -3346,6 +3376,11 @@ shaka.hls.HlsParser = class {
       presentationDelay = this.maxTargetDuration_ * delaySegments;
     }
 
+    if (this.startTime_ && this.startTime_ < 0) {
+      presentationDelay = Math.min(-this.startTime_, presentationDelay);
+      this.startTime_ += presentationDelay;
+    }
+
     this.presentationTimeline_.setPresentationStartTime(0);
     this.presentationTimeline_.setDelay(presentationDelay);
     this.presentationTimeline_.setStatic(false);

lib/mss/mss_parser.js

@@ -429,6 +429,7 @@ shaka.mss.MssParser = class {
         periodCount: 1,
         gapCount: 0,
         isLowLatency: false,
+        startTime: null,
       };
 
       // This is the first point where we have a meaningful presentation start

lib/offline/manifest_converter.js

@@ -97,6 +97,7 @@ shaka.offline.ManifestConverter = class {
       periodCount: 1,
       gapCount: 0,
       isLowLatency: false,
+      startTime: null,
     };
   }
 

lib/player.js

@@ -2509,7 +2509,11 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     };
 
     if (!this.config_.streaming.startAtSegmentBoundary) {
-      setupPlayhead(this.startTime_);
+      let startTime = this.startTime_;
+      if (startTime == null && this.manifest_.startTime) {
+        startTime = this.manifest_.startTime;
+      }
+      setupPlayhead(startTime);
     }
 
     // Now we can switch to the initial variant.
@@ -2522,6 +2526,9 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       if (this.config_.streaming.startAtSegmentBoundary) {
         const timeline = this.manifest_.presentationTimeline;
         let initialTime = this.startTime_ || this.video_.currentTime;
+        if (this.startTime_ == null && this.manifest_.startTime) {
+          initialTime = this.manifest_.startTime;
+        }
         const seekRangeStart = timeline.getSeekRangeStart();
         const seekRangeEnd = timeline.getSeekRangeEnd();
         if (initialTime < seekRangeStart) {

roadmap.md

@@ -22,6 +22,7 @@ v5.0 - 2024 Q4
 
 v4.11 - 2024 Q3
  - HLS improvements
+ - HLS: EXT-X-START support
 
 =====
 

test/hls/hls_live_unit.js

@@ -570,6 +570,31 @@ describe('HlsParser live', () => {
           expect(manifest.presentationTimeline.getDelay()).toBe(15);
         });
 
+    it('sets 3 times target duration as presentation delay if not configured and clamped to the start', async () => { // eslint-disable-line max-len
+      const media = [
+        '#EXTM3U\n',
+        '#EXT-X-TARGETDURATION:5\n',
+        '#EXT-X-START:TIME-OFFSET=-10\n',
+        '#EXT-X-MAP:URI="init.mp4",BYTERANGE="616@0"\n',
+        '#EXT-X-MEDIA-SEQUENCE:0\n',
+        '#EXTINF:2,\n',
+        'main.mp4\n',
+        '#EXTINF:2,\n',
+        'main.mp4\n',
+        '#EXTINF:2,\n',
+        'main.mp4\n',
+        '#EXTINF:2,\n',
+        'main.mp4\n',
+        '#EXTINF:2,\n',
+        'main.mp4\n',
+        '#EXTINF:2,\n',
+        'main.mp4\n',
+      ].join('');
+      const manifest = await testInitialManifest(master, media);
+      expect(manifest.presentationTimeline.getDelay()).toBe(10);
+      expect(manifest.startTime).toBe(0);
+    });
+
     it('sets 1 times target duration as presentation delay if there are not enough segments', async () => { // eslint-disable-line max-len
       const media = [
         '#EXTM3U\n',

test/hls/hls_parser_unit.js

@@ -156,6 +156,7 @@ describe('HlsParser', () => {
   it('parses manifest attributes', async () => {
     const master = [
       '#EXTM3U\n',
+      '#EXT-X-START:TIME-OFFSET=2\n',
       '#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aud1",LANGUAGE="eng",',
       'CHANNELS="16/JOC",SAMPLE-RATE="48000",URI="audio"\n',
       '#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="sub1",LANGUAGE="eng",',
@@ -187,6 +188,7 @@ describe('HlsParser', () => {
     const manifest = shaka.test.ManifestGenerator.generate((manifest) => {
       manifest.sequenceMode = sequenceMode;
       manifest.type = shaka.media.ManifestParser.HLS;
+      manifest.startTime = 2;
       manifest.anyTimeline();
       manifest.addPartialVariant((variant) => {
         variant.language = 'en';
@@ -5081,6 +5083,7 @@ describe('HlsParser', () => {
   it('parses media playlists directly', async () => {
     const media = [
       '#EXTM3U\n',
+      '#EXT-X-START:TIME-OFFSET=-2\n',
       '#EXT-X-PLAYLIST-TYPE:VOD\n',
       '#EXT-X-MAP:URI="init.mp4",BYTERANGE="616@0"\n',
       '#EXTINF:5,\n',
@@ -5091,6 +5094,7 @@ describe('HlsParser', () => {
     const manifest = shaka.test.ManifestGenerator.generate((manifest) => {
       manifest.sequenceMode = sequenceMode;
       manifest.type = shaka.media.ManifestParser.HLS;
+      manifest.startTime = -2;
       manifest.anyTimeline();
       manifest.addPartialVariant((variant) => {
         variant.addPartialStream(ContentType.VIDEO, (stream) => {

test/media/playhead_unit.js

@@ -141,6 +141,7 @@ describe('Playhead', () => {
       periodCount: 1,
       gapCount: 0,
       isLowLatency: false,
+      startTime: null,
     };
 
     config = shaka.util.PlayerConfiguration.createDefault().streaming;

test/media/streaming_engine_integration.js

@@ -609,6 +609,7 @@ describe('StreamingEngine', () => {
         periodCount: 1,
         gapCount: 0,
         isLowLatency: false,
+        startTime: null,
         variants: [{
           id: 1,
           video: {

test/test/util/manifest_generator.js

@@ -111,6 +111,8 @@ shaka.test.ManifestGenerator.Manifest = class {
     this.gapCount = 0;
     /** @type {boolean} */
     this.isLowLatency = false;
+    /** @type {?number} */
+    this.startTime = null;
 
 
     /** @type {shaka.extern.Manifest} */

test/test/util/streaming_engine_util.js

@@ -324,6 +324,7 @@ shaka.test.StreamingEngineUtil = class {
       periodCount: 1,
       gapCount: 0,
       isLowLatency: false,
+      startTime: null,
     };
 
     /** @type {shaka.extern.Variant} */