This release includes the following changes since the 1.3.1 release:

• ExoPlayer:
  • Add BasePreloadManager which coordinates the preloading for multiple sources based on the priorities defined by their rankingData. Customization is possible by extending this class. Add DefaultPreloadManager which uses PreloadMediaSource to preload media samples of the sources into memory, and uses an integer rankingData that indicates the index of an item on the UI.
  • Add PlayerId to most methods of LoadControl to enable LoadControl implementations to support multiple players.
  • Remove Buffer.isDecodeOnly() and C.BUFFER_FLAG_DECODE_ONLY. There is no need to set this flag as renderers and decoders will decide to skip buffers based on timestamp. Custom Renderer implementations should check if the buffer time is at least BaseRenderer.getLastResetPositionUs() to decide whether a sample should be shown. Custom SimpleDecoder implementations can check isAtLeastOutputStartTimeUs if needed or mark other buffers with DecoderOutputBuffer.shouldBeSkipped to skip them.
  • Allow a null value to be returned by TargetPreloadStatusControl.getTargetPreloadStatus(T) to indicate not to preload a MediaSource with the given rankingData.
  • Add remove(MediaSource) to BasePreloadManager.
• Transformer:
  • Add audioConversionProcess and videoConversionProcess to ExportResult indicating how the respective track in the output file was made.
  • Relax trim optimization H.264 level checks.
  • Add support for changing between SDR and HDR input media in a sequence.
  • Add support for composition-level audio effects.
  • Add support for transcoding Ultra HDR images into HDR videos.
  • Fix issue where the DefaultAudioMixer does not output the correct amount of bytes after being reset and reused.
• Video:
  • Fix issue where Listener.onRenderedFirstFrame() arrives too early when switching surfaces mid-playback.
• DataSource:
  • Implement support for android.resource://package/id raw resource URIs where package is different to the package of the current application. This wasn't previously documented to work, but is a more efficient way of accessing resources in another package than by name.
  • Eagerly check url is non-null in the DataSpec constructors. This parameter was already annotated to be non-null.
• Effect:
  • Support multiple speed changes within the same EditedMediaItem or Composition in SpeedChangeEffect.
  • Support for HLG and PQ output from ultra HDR bitmap input.
  • Add support for EGL_GL_COLORSPACE_BT2020_HLG_EXT, which improves HLG surface output in ExoPlayer.setVideoEffect and Transformer's Debug SurfaceView.
  • Update Overlay matrix implementation to make it consistent with the documentation by flipping the x and y values applied in setOverlayFrameAnchor(). If using OverlaySettings.Builder.setOverlayFrameAnchor(), flip their x and y values by multiplying them by -1.
• Session:
  • Change default of CommandButton.enabled to true and ensure the value can stay false for controllers even if the associated command is available.
  • Add icon constants for CommandButton that should be used instead of custom icon resources.
  • Add MediaSessionService.isPlaybackOngoing() to let apps query whether the service needs to be stopped in onTaskRemoved() (#1219).
  • Add MediaSessionService.pauseAllPlayersAndStopSelf() that conveniently allows to pause playback of all sessions and call stopSelf to terminate the lifecycle of the MediaSessionService.
  • Override MediaSessionService.onTaskRemoved(Intent) to provide a safe default implementation that keeps the service running in the foreground if playback is ongoing or stops the service otherwise.
• Downloads:
  • Ensure that DownloadHelper does not leak unreleased Renderer instances, which can eventually result in an app crashing with IllegalStateException: Too many receivers, total of 1000, registered for pid (#1224).
• Test Utilities:
  • Implement onInit() and onRelease() in FakeRenderer.
  • Change TestPlayerRunHelper.runUntil/playUntil methods to fail on nonfatal errors (e.g. those reported to AnalyticsListener.onVideoCodecError). Use the new TestPlayerRunHelper.run(player).ignoringNonFatalErrors().untilXXX() method chain to disable this behavior.
• Demo app:
  • Use DefaultPreloadManager in the short form demo app.
• Remove deprecated symbols:
  • Remove CronetDataSourceFactory. Use CronetDataSource.Factory instead.
  • Remove some DataSpec constructors. Use DataSpec.Builder instead.