Let ExoPlayer handle video looping seamlessly

Now that videos are replacing the inefficient GIF format, gapless loops are
important. ExoPlayer's built-in mechanism prebuffers the video to enable this,
whereas the current implementation of seeking to the start presents a short but
noticeable delay between each loop.

Note that this change introduces an incompatibility with current behaviour: due
to google/ExoPlayer#6459, certain videos with broken audio tracks that played
fine before will no longer start. Disabling the audio track is a workaround to
re-enable looping playback, but ExoPlayer does not appear to expose a way to
check if the audio track is short enough to produce the bug.

app/src/main/kotlin/com/simplemobiletools/gallery/pro/activities/VideoPlayerActivity.kt

@@ -214,6 +214,9 @@ open class VideoPlayerActivity : SimpleActivity(), SeekBar.OnSeekBarChangeListen
         mExoPlayer = ExoPlayerFactory.newSimpleInstance(applicationContext).apply {
             seekParameters = SeekParameters.CLOSEST_SYNC
             audioStreamType = C.STREAM_TYPE_MUSIC
+            if (config.loopVideos) {
+                repeatMode = Player.REPEAT_MODE_ONE
+            }
             prepare(audioSource)
         }
         initExoPlayerListeners()

app/src/main/kotlin/com/simplemobiletools/gallery/pro/fragments/VideoFragment.kt

@@ -317,6 +317,9 @@ class VideoFragment : ViewPagerFragment(), TextureView.SurfaceTextureListener, S
 
         mExoPlayer = ExoPlayerFactory.newSimpleInstance(context)
         mExoPlayer!!.seekParameters = SeekParameters.CLOSEST_SYNC
+        if (mConfig.loopVideos) {
+            mExoPlayer?.repeatMode = Player.REPEAT_MODE_ONE
+        }
 
         val isContentUri = mMedium.path.startsWith("content://")
         val uri = if (isContentUri) Uri.parse(mMedium.path) else Uri.fromFile(File(mMedium.path))