fix: Handle updateend event on duration reduction (#8403)

https://www.w3.org/TR/media-source-2/#duration-change-algorithm
"Duration reductions that would truncate currently buffered media are
disallowed.
When truncation is necessary, use remove() to reduce the buffered range
before updating duration."
Introduced a new config durationReductionEmitsUpdateEnd. When set
indicates media source duration change can truncate buffer, hence
updateend event is expected on setDuration operation if new duration is
smaller than existing value. Disabled by default to match W3C specs.

---------

Co-authored-by: Srikanth Peddibhotla <[email protected]>
Co-authored-by: Álvaro Velad Galván <[email protected]>
Co-authored-by: theodab <[email protected]>

Author: 4 people

demo/config.js

@@ -702,7 +702,9 @@ shakaDemo.Config = class {
         .addBoolInput_('Dispatch all emsg boxes',
             'mediaSource.dispatchAllEmsgBoxes')
         .addBoolInput_('Uses source elements',
-            'mediaSource.useSourceElements');
+            'mediaSource.useSourceElements')
+        .addBoolInput_('Expect updateEnd when duration is truncated',
+            'mediaSource.durationReductionEmitsUpdateEnd');
   }
 
   /** @private */

externs/shaka/player.js

@@ -2185,7 +2185,8 @@ shaka.extern.NetworkingConfiguration;
  *   insertFakeEncryptionInInit: boolean,
  *   modifyCueCallback: shaka.extern.TextParser.ModifyCueCallback,
  *   dispatchAllEmsgBoxes: boolean,
- *   useSourceElements: boolean
+ *   useSourceElements: boolean,
+ *   durationReductionEmitsUpdateEnd: boolean
  * }}
  *
  * @description
@@ -2234,6 +2235,17 @@ shaka.extern.NetworkingConfiguration;
  *   Disabling it will prevent using AirPlay on MSE.
  *   <br>
  *   Defaults to <code>true</code>.
+ * @property {boolean} durationReductionEmitsUpdateEnd
+ *   https://www.w3.org/TR/media-source-2/#duration-change-algorithm
+ *   "Duration reductions that would truncate currently buffered media are
+ *   disallowed.
+ *   When truncation is necessary, use remove() to reduce the buffered range
+ *   before updating duration."
+ *   When set indicates media source duration change can truncate buffer, hence
+ *   updateend event is expected on setDuration operation if new duration is
+ *   smaller than existing value.
+ *   <br>
+ *   Defaults to <code>true</code>.
  * @exportDoc
  */
 shaka.extern.MediaSourceConfiguration;

lib/media/media_source_engine.js

@@ -1678,11 +1678,20 @@ shaka.media.MediaSourceEngine = class {
    */
   async setDuration(duration) {
     await this.enqueueBlockingOperation_(() => {
-      // Reducing the duration causes the MSE removal algorithm to run, which
-      // triggers an 'updateend' event to fire.  To handle this scenario, we
-      // have to insert a dummy operation into the beginning of each queue,
-      // which the 'updateend' handler will remove.
-      if (duration < this.mediaSource_.duration) {
+      // https://www.w3.org/TR/media-source-2/#duration-change-algorithm
+      // "Duration reductions that would truncate currently buffered media
+      // are disallowed.
+      // When truncation is necessary, use remove() to reduce the buffered
+      // range before updating duration."
+      // But in some platforms, truncating the duration causes the
+      // buffer range removal algorithm to run which triggers an
+      // 'updateend' event to fire.
+      // To handle this scenario, we have to insert a dummy operation into
+      // the beginning of each queue, which the 'updateend' handler will remove.
+      // Using config to disable it by default and enable only
+      // on relevant platforms.
+      if (this.config_.durationReductionEmitsUpdateEnd &&
+                duration < this.mediaSource_.duration) {
         for (const contentType of this.sourceBuffers_.keys()) {
           const dummyOperation = {
             start: () => {},

lib/util/player_configuration.js

@@ -431,6 +431,7 @@ shaka.util.PlayerConfiguration = class {
       },
       dispatchAllEmsgBoxes: false,
       useSourceElements: true,
+      durationReductionEmitsUpdateEnd: true,
     };
 
     let customPlayheadTracker = false;