feat(HLS): Add support to HOLD-BACK in EXT-X-SERVER-CONTROL (#5281)

shaka-project · Jun 12, 2023 · bb2c06a · bb2c06a
1 parent 090554b
commit bb2c06a
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Showing 2 changed files with 30 additions and 3 deletions.
diff --git a/lib/hls/hls_parser.js b/lib/hls/hls_parser.js
@@ -185,6 +185,9 @@ shaka.hls.HlsParser = class {
      */
     this.partialTargetDuration_ = 0;
 
+    /** @private {number} */
+    this.presentationDelay_ = 0;
+
     /** @private {number} */
     this.lowLatencyPresentationDelay_ = 0;
 
@@ -2621,6 +2624,9 @@ shaka.hls.HlsParser = class {
     const targetDuration = Number(targetDurationTag.value);
     const partialTargetDurationTag =
       shaka.hls.Utils.getFirstTagWithName(playlist.tags, 'EXT-X-PART-INF');
+    // Get the server-recommended min distance from the live edge.
+    const serverControlTag = shaka.hls.Utils.getFirstTagWithName(
+        playlist.tags, 'EXT-X-SERVER-CONTROL');
     // According to the HLS spec, updates should not happen more often than
     // once in targetDuration.  It also requires us to only update the active
     // variant.  We might implement that later, but for now every variant
@@ -2634,9 +2640,6 @@ shaka.hls.HlsParser = class {
           partialTargetDurationTag.getRequiredAttrValue('PART-TARGET'));
       this.lastTargetDuration_ = Math.min(
           this.partialTargetDuration_, this.lastTargetDuration_);
-      // Get the server-recommended min distance from the live edge.
-      const serverControlTag = shaka.hls.Utils.getFirstTagWithName(
-          playlist.tags, 'EXT-X-SERVER-CONTROL');
       // Use 'PART-HOLD-BACK' as the presentation delay for low latency mode.
       this.lowLatencyPresentationDelay_ = serverControlTag ? Number(
           serverControlTag.getRequiredAttrValue('PART-HOLD-BACK')) : 0;
@@ -2656,6 +2659,10 @@ shaka.hls.HlsParser = class {
       }
       this.lastTargetDuration_ = Math.min(
           lastTargetDuration, this.lastTargetDuration_);
+      // Use 'HOLD-BACK' as the presentation delay for default if defined.
+      const holdBack = serverControlTag ?
+          serverControlTag.getAttribute('HOLD-BACK') : null;
+      this.presentationDelay_ = holdBack ? Number(holdBack.value) : 0;
     }
     // 2. Update the longest target duration if need be to use as a
     // presentation delay later.
@@ -2687,6 +2694,8 @@ shaka.hls.HlsParser = class {
       presentationDelay = this.config_.defaultPresentationDelay;
     } else if (this.lowLatencyPresentationDelay_) {
       presentationDelay = this.lowLatencyPresentationDelay_;
+    } else if (this.presentationDelay_) {
+      presentationDelay = this.presentationDelay_;
     } else {
       const numberOfSegments = this.config_.hls.liveSegmentsDelay;
       presentationDelay = this.maxTargetDuration_ * numberOfSegments;

diff --git a/test/hls/hls_live_unit.js b/test/hls/hls_live_unit.js
@@ -544,6 +544,24 @@ describe('HlsParser live', () => {
           expect(manifest.presentationTimeline.getDelay()).toBe(15);
         });
 
+    it('sets presentation delay if defined', async () => {
+      const media = [
+        '#EXTM3U\n',
+        '#EXT-X-SERVER-CONTROL:HOLD-BACK=2\n',
+        '#EXT-X-TARGETDURATION:5\n',
+        '#EXT-X-PART-INF:PART-TARGET=0.5\n',
+        '#EXT-X-MAP:URI="init.mp4",BYTERANGE="616@0"\n',
+        '#EXT-X-MEDIA-SEQUENCE:0\n',
+        '#EXTINF:2,\n',
+        'main.mp4\n',
+      ].join('');
+
+      const manifest = await testInitialManifest(master, media);
+      // Presentation delay should be the value of 'HOLD-BACK' if not
+      // configured.
+      expect(manifest.presentationTimeline.getDelay()).toBe(2);
+    });
+
     it('sets presentation delay for low latency mode', async () => {
       const mediaWithLowLatency = [
         '#EXTM3U\n',