Fix internal seek (Dash-Industry-Forum#3536)

* When doing internal seek, re-enable 'seeking' listener once currentTime has been set (do not wait for 'seeked' event)

* for internal seek, do not disable 'seeking' listener, but simply ignore next 'seeking' event after internal seek, so that concurrent user seeks can be considered (without waiting for 'seeked' event)

src/streaming/controllers/PlaybackController.js

@@ -60,6 +60,7 @@ function PlaybackController() {
         lastLivePlaybackTime,
         availabilityStartTime,
         seekTarget,
+        internalSeek,
         isLowLatencySeekingInProgress,
         playbackStalled,
         minPlaybackRateChange,
@@ -80,6 +81,7 @@ function PlaybackController() {
         playbackStalled = false;
         streamSwitch = periodSwitch === true;
         streamSeekTime = seekTime;
+        internalSeek = false;
 
         const ua = typeof navigator !== 'undefined' ? navigator.userAgent.toLowerCase() : '';
 
@@ -176,24 +178,20 @@ function PlaybackController() {
         return streamInfo && videoModel ? videoModel.isSeeking() : null;
     }
 
-    function seek(time, stickToBuffered, internalSeek) {
+    function seek(time, stickToBuffered, internal) {
         if (!streamInfo || !videoModel) return;
 
         let currentTime = !isNaN(seekTarget) ? seekTarget : videoModel.getTime();
         if (time === currentTime) return;
 
-        if (internalSeek === true) {
-            // Internal seek = seek video model only (disable 'seeking' listener)
-            // buffer(s) are already appended at requested time
-            videoModel.removeEventListener('seeking', onPlaybackSeeking);
-            logger.info('Requesting internal seek to time: ' + time);
-            videoModel.setCurrentTime(time, stickToBuffered);
-        } else {
+        internalSeek = (internal === true);
+
+        if (!internalSeek) {
             seekTarget = time;
             eventBus.trigger(Events.PLAYBACK_SEEK_ASKED);
-            logger.info('Requesting seek to time: ' + time);
-            videoModel.setCurrentTime(time, stickToBuffered);
         }
+        logger.info('Requesting seek to time: ' + time + (internalSeek ? ' (internal)' : ''));
+        videoModel.setCurrentTime(time, stickToBuffered);
     }
 
     function seekToLive() {
@@ -484,6 +482,12 @@ function PlaybackController() {
     }
 
     function onPlaybackSeeking() {
+        // Check if internal seeking to be ignored
+        if (internalSeek) {
+            internalSeek = false;
+            return;
+        }
+
         let seekTime = getTime();
         // On some browsers/devices, in case of live streams, setting current time on video element fails when there is no buffered data at requested time
         // Then re-set seek target time and video element will be seeked afterwhile once data is buffered (see BufferContoller)
@@ -500,8 +504,6 @@ function PlaybackController() {
     function onPlaybackSeeked() {
         logger.info('Native video element event: seeked');
         eventBus.trigger(Events.PLAYBACK_SEEKED);
-        // Reactivate 'seeking' event listener (see seek())
-        videoModel.addEventListener('seeking', onPlaybackSeeking);
     }
 
     function onPlaybackTimeUpdated() {