Expose additional metrics for low latency (#387)

* Expose PLAYBACK_RATE_CHANGED to the plugin interface

* Expose latency info to onPlayerInfoUpdated

Author: ryanmccartney

.releasinator.json

@@ -5,4 +5,4 @@
   "displayPattern": "$.$.$",
   "enforceUserFacingLabel": false,
   "projectType": "npm-like"
-}
+}

src/playbackstrategy/msestrategy.js

@@ -85,6 +85,7 @@ function MSEStrategy(
     },
     playbackBitrate: undefined,
     bufferLength: undefined,
+    latency: undefined,
     fragmentInfo: {
       requestTime: undefined,
       numDownloaded: undefined,
@@ -115,6 +116,7 @@ function MSEStrategy(
     QUOTA_EXCEEDED: "quotaExceeded",
     TEXT_TRACKS_ADDED: "allTextTracksAdded",
     CURRENT_TRACK_CHANGED: "currentTrackChanged",
+    PLAYBACK_RATE_CHANGED: "playbackRateChanged",
   }
 
   function onLoadedMetaData() {
@@ -344,6 +346,7 @@ function MSEStrategy(
     Plugins.interface.onPlayerInfoUpdated({
       bufferLength: playerMetadata.bufferLength,
       playbackBitrate: playerMetadata.playbackBitrate,
+      latency: playerMetadata.latency,
     })
   }
 
@@ -480,11 +483,13 @@ function MSEStrategy(
       dashMetrics = mediaPlayer.getDashMetrics()
 
       if (dashMetrics) {
+        playerMetadata.latency = mediaPlayer.getCurrentLiveLatency()
         playerMetadata.bufferLength = dashMetrics.getCurrentBufferLevel(event.mediaType)
         DebugTool.staticMetric("buffer-length", playerMetadata.bufferLength)
         Plugins.interface.onPlayerInfoUpdated({
           bufferLength: playerMetadata.bufferLength,
           playbackBitrate: playerMetadata.playbackBitrate,
+          latency: playerMetadata.latency,
         })
       }
     }
@@ -692,6 +697,11 @@ function MSEStrategy(
     mediaPlayer.on(DashJSEvents.TEXT_TRACKS_ADDED, handleTextTracks)
     mediaPlayer.on(DashJSEvents.MANIFEST_LOADING_FINISHED, manifestLoadingFinished)
     mediaPlayer.on(DashJSEvents.CURRENT_TRACK_CHANGED, onCurrentTrackChanged)
+    mediaPlayer.on(DashJSEvents.PLAYBACK_RATE_CHANGED, onPlaybackRateChanged)
+  }
+
+  function onPlaybackRateChanged(event) {
+    Plugins.interface.onPlaybackRateChanged(event)
   }
 
   function handleTextTracks() {
@@ -880,7 +890,7 @@ function MSEStrategy(
       mediaPlayer.off(DashJSEvents.GAP_JUMP_TO_END, onGapJump)
       mediaPlayer.off(DashJSEvents.QUOTA_EXCEEDED, onQuotaExceeded)
       mediaPlayer.off(DashJSEvents.CURRENT_TRACK_CHANGED, onCurrentTrackChanged)
-
+      mediaPlayer.off(DashJSEvents.PLAYBACK_RATE_CHANGED, onPlaybackRateChanged)
       mediaPlayer = undefined
     }
 

src/playbackstrategy/msestrategy.test.js

@@ -646,6 +646,7 @@ describe("Media Source Extensions Playback Strategy", () => {
 
       expect(Plugins.interface.onPlayerInfoUpdated).toHaveBeenCalledWith({
         playbackBitrate: undefined,
+        latency: undefined,
         bufferLength: 15,
       })
     })

src/plugins.js

@@ -50,5 +50,6 @@ export default {
     onSubtitlesDynamicLoadError: (evt) => callOnAllPlugins("onSubtitlesDynamicLoadError", evt),
     onFragmentContentLengthMismatch: (evt) => callOnAllPlugins("onFragmentContentLengthMismatch", evt),
     onQuotaExceeded: (evt) => callOnAllPlugins("onQuotaExceeded", evt),
+    onPlaybackRateChanged: (evt) => callOnAllPlugins("onPlaybackRateChanged", evt),
   },
 }