feat(DASH): Add support for minimum values in service descriptions (#…

…5844)

Closes #5780

demo/config.js

@@ -407,6 +407,14 @@ shakaDemo.Config = class {
         .addNumberInput_('Playback rate for live sync',
             'streaming.liveSyncPlaybackRate',
             /* canBeDecimal= */ true,
+            /* canBeZero= */ false)
+        .addNumberInput_('Min latency for live sync',
+            'streaming.liveSyncMinLatency',
+            /* canBeDecimal= */ true,
+            /* canBeZero= */ true)
+        .addNumberInput_('Min playback rate for live sync',
+            'streaming.liveSyncMinPlaybackRate',
+            /* canBeDecimal= */ true,
             /* canBeZero= */ false);
 
     if (!shakaDemoMain.getNativeControlsEnabled()) {

externs/shaka/manifest.js

@@ -152,18 +152,26 @@ shaka.extern.InitDataOverride;
 /**
  * @typedef {{
  *   maxLatency: ?number,
- *   maxPlaybackRate: ?number
+ *   maxPlaybackRate: ?number,
+ *   minLatency: ?number,
+ *   minPlaybackRate: ?number
  * }}
  *
  * @description
- * Maximum latency and playback rate for a manifest. When max latency is reached
- * playbackrate is updated to maxPlaybackRate to decrease latency.
+ * Maximum and minimun latency and playback rate for a manifest. When max
+ * latency is reached playbackrate is updated to maxPlaybackRate to decrease
+ * latency. When min  latency is reached playbackrate is updated to
+ * minPlaybackRate to increase  latency.
  * More information {@link https://dashif.org/docs/CR-Low-Latency-Live-r8.pdf here}.
  *
  * @property {?number} maxLatency
  *  Maximum latency in seconds.
  * @property {?number} maxPlaybackRate
  *  Maximum playback rate.
+ * @property {?number} minLatency
+ *  Minimun latency in seconds.
+ * @property {?number} minPlaybackRate
+ *  Minimun playback rate.
  *
  * @exportDoc
  */

externs/shaka/player.js

@@ -1105,7 +1105,9 @@ shaka.extern.ManifestConfiguration;
  *   segmentPrefetchLimit: number,
  *   liveSync: boolean,
  *   liveSyncMaxLatency: number,
- *   liveSyncPlaybackRate: number
+ *   liveSyncPlaybackRate: number,
+ *   liveSyncMinLatency: number,
+ *   liveSyncMinPlaybackRate: number
  * }}
  *
  * @description
@@ -1234,6 +1236,13 @@ shaka.extern.ManifestConfiguration;
  *   Playback rate used for latency chasing. It is recommended to use a value
  *   between 1 and 2. Effective only if liveSync is true. Defaults to
  *   <code>1.1</code>.
+ * @property {number} liveSyncMinLatency
+ *   Minimun acceptable latency, in seconds. Effective only if liveSync is
+ *   true. Defaults to <code>0</code>.
+ * @property {number} liveSyncMinPlaybackRate
+ *   Minimun playback rate used for latency chasing. It is recommended to use a
+ *   value between 0 and 1. Effective only if liveSync is true. Defaults to
+ *   <code>1</code>.
  * @exportDoc
  */
 shaka.extern.StreamingConfiguration;

lib/dash/dash_parser.js

@@ -603,8 +603,19 @@ shaka.dash.DashParser = class {
       const maxPlaybackRate = playbackRateNode ?
         parseFloat(playbackRateNode.getAttribute('max')) :
         null;
+      const minLatency = latencyNode && latencyNode.getAttribute('min') ?
+        parseInt(latencyNode.getAttribute('min'), 10) / 1000 :
+        null;
+      const minPlaybackRate = playbackRateNode ?
+        parseFloat(playbackRateNode.getAttribute('min')) :
+        null;
 
-      return {maxLatency, maxPlaybackRate};
+      return {
+        maxLatency,
+        maxPlaybackRate,
+        minLatency,
+        minPlaybackRate,
+      };
     }
 
     return null;

lib/player.js

@@ -5471,6 +5471,23 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       }
     }
 
+    let liveSyncMinLatency;
+    let liveSyncMinPlaybackRate;
+    if (this.config_.streaming.liveSync) {
+      liveSyncMinLatency = this.config_.streaming.liveSyncMinLatency;
+      liveSyncMinPlaybackRate = this.config_.streaming.liveSyncMinPlaybackRate;
+    } else {
+      // serviceDescription must override if it is defined in the MPD and
+      // liveSync configuration is not set.
+      if (this.manifest_ && this.manifest_.serviceDescription) {
+        liveSyncMinLatency = this.manifest_.serviceDescription.minLatency ||
+          this.config_.streaming.liveSyncMinLatency;
+        liveSyncMinPlaybackRate =
+          this.manifest_.serviceDescription.minPlaybackRate ||
+          this.config_.streaming.liveSyncMinPlaybackRate;
+      }
+    }
+
     const playbackRate = this.video_.playbackRate;
     const latency = seekRange.end - this.video_.currentTime;
     let offset = 0;
@@ -5494,6 +5511,14 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
           'Updating playbackRate to ' + liveSyncPlaybackRate);
         this.trickPlay(liveSyncPlaybackRate);
       }
+    } else if (liveSyncMinLatency && liveSyncMinPlaybackRate &&
+        (latency - offset) < liveSyncMinLatency) {
+      if (playbackRate != liveSyncMinPlaybackRate) {
+        shaka.log.debug('Latency (' + latency + 's) ' +
+          'is smaller than liveSyncMinLatency (' + liveSyncMinLatency + 's). ' +
+          'Updating playbackRate to ' + liveSyncMinPlaybackRate);
+        this.trickPlay(liveSyncMinPlaybackRate);
+      }
     } else if (playbackRate !== this.playRateController_.getDefaultRate()) {
       this.cancelTrickPlay();
     }

lib/util/player_configuration.js

@@ -216,6 +216,8 @@ shaka.util.PlayerConfiguration = class {
       liveSync: false,
       liveSyncMaxLatency: 1,
       liveSyncPlaybackRate: 1.1,
+      liveSyncMinLatency: 0,
+      liveSyncMinPlaybackRate: 1,
     };
 
     // WebOS, Tizen, Chromecast and Hisense have long hardware pipelines

test/dash/dash_parser_manifest_unit.js

@@ -2611,8 +2611,8 @@ describe('DashParser Manifest', () => {
         '<MPD minBufferTime="PT75S" type="dynamic"',
         '     availabilityStartTime="1970-01-01T00:00:00Z">',
         '  <ServiceDescription id="0">',
-        '    <Latency max="2000" min="2000" referenceId="0" target="4000" />',
-        '    <PlaybackRate max="1.10" min="0.96" />',
+        '    <Latency max="2000" min="1000" referenceId="0" target="4000" />',
+        '    <PlaybackRate max="1.10" min="0.95" />',
         '  </ServiceDescription>',
         '</MPD>',
       ].join('\n');
@@ -2624,6 +2624,8 @@ describe('DashParser Manifest', () => {
 
       expect(manifest.serviceDescription.maxLatency).toBe(2);
       expect(manifest.serviceDescription.maxPlaybackRate).toBe(1.1);
+      expect(manifest.serviceDescription.minLatency).toBe(1);
+      expect(manifest.serviceDescription.minPlaybackRate).toBe(0.95);
     });
   });
 });