feat: Add safeSeekEndOffset feature for live reposition (#7532)

Close #7531

demo/config.js

@@ -468,6 +468,8 @@ shakaDemo.Config = class {
             /* canBeDecimal= */ true)
         .addNumberInput_('Safe Seek Offset', 'streaming.safeSeekOffset',
             /* canBeDecimal= */ true)
+        .addNumberInput_('Safe Seek Offset', 'streaming.safeSeekEndOffset',
+            /* canBeDecimal= */ true)
         .addNumberInput_('Stall Threshold', 'streaming.stallThreshold',
             /* canBeDecimal= */ true)
         .addNumberInput_('Safe Skip Distance', 'streaming.stallSkip',

externs/shaka/player.js

@@ -1550,6 +1550,7 @@ shaka.extern.LiveSyncConfiguration;
  *   gapJumpTimerTime: number,
  *   durationBackoff: number,
  *   safeSeekOffset: number,
+ *   safeSeekEndOffset: number,
  *   stallEnabled: boolean,
  *   stallThreshold: number,
  *   stallSkip: number,
@@ -1666,6 +1667,13 @@ shaka.extern.LiveSyncConfiguration;
  *   bandwidth scenarios.
  *   <br>
  *   Defaults to <code>5</code>.
+ * @property {number} safeSeekEndOffset
+ *   The amount of seconds that should be added when repositioning the playhead
+ *   after falling out of the seakable end range. This is helpful for live
+ *   stream with a lot of GAP. This will reposition the playback in the past
+ *   and avoid to be block at the edge and buffer at the next GAP
+ *   <br>
+ *   Defaults to <code>0</code>.
  * @property {boolean} stallEnabled
  *   When set to <code>true</code>, the stall detector logic will run.  If the
  *   playhead stops moving for <code>stallThreshold</code> seconds, the player

lib/media/playhead.js

@@ -517,7 +517,9 @@ shaka.media.MediaSourcePlayhead = class {
 
     if (currentTime > end) {
       shaka.log.v1('Playhead past end.');
-      return end;
+      // We remove the safeSeekEndOffset of the seek end to avoid the player
+      // to be block at the edge in a live stream
+      return end - this.config_.safeSeekEndOffset;
     }
 
     if (currentTime < start) {

lib/util/player_configuration.js

@@ -218,6 +218,7 @@ shaka.util.PlayerConfiguration = class {
       // Offset by 5 seconds since Chromecast takes a few seconds to start
       // playing after a seek, even when buffered.
       safeSeekOffset: 5,
+      safeSeekEndOffset: 0,
       stallEnabled: true,
       stallThreshold: 1 /* seconds */,
       stallSkip: 0.1 /* seconds */,