SDK / exoplayer

Issue: #689

When ChunkSource implementations implement multi-track for DASH and SS,
format selection will move inside of ChunkSource. If we, for example, fail
to query the decoder to determine which tracks are playable, we need an
opportunity to fail (i.e. say we're not prepared, so that maybeThrowError
is called, from which we can throw).

This may go away in the future if we remove the distinct preparation step
and treat tracks/formats as things that can change dynamically, but for now
this is what we have.

Issue #514.

Fix reading the first slice flag, which before could cause a read out of bounds
if the NAL unit started at the end of the buffer.

Handle non-VCL NAL units by flushing a pending sample when starting to read one.

Issue: 713

Also:
- Better document MediaFormat.
- Document getFormat to indicate what it's good (and not good) for.

multi-track support upstream to the ChunkSource interface.

This change does not yet make use of the newly exposed APIs. This
will come in a subsequent CL.

Issue #514.

- Currently all subtitles we parse contain timestamps relative to the sample
  timestamp, however we add the sample timestamp in inconsistent ways (sometimes
  in the Subtitle, sometimes in the SubtitleParser). This change converges on
  a single approach. It also paves the way for passing absolute offsets to use
  instead, and being able to apply them in a consistent way in a single place
  (PlayableSubtitle). This functionality will be required for ISO 14496-30 TTML
  embedded subtitles.

Issue: #689

Issue #587

Issue: #91

Issue #514.

Issue: #697

- Parse all attributes that may exist in either the AdaptationSet or
  in the child Representation elements at both levels.
- Correctly infer TYPE_TEXT for Representation elements whose mimeType
  is application/mp4 and whose codecs attribute indicates a known text
  codec type.

Issue: #689

+ Move conversion from framework -> exo format to FrameworkSampleSource.
+ Improve MediaFormat conversion test.

Remove MPEG TS stream filtering based on AudioCapabilities.

Pass AudioCapabilities to MediaCodecAudioTrackRenderer so it can choose between
passthrough/raw and decoding for AC-3 tracks.

- Generalize rendererEnabledFlags to be selected track indices through
  ExoPlayerImpl/ExoPlayerImplInternal.
- Selecting an out-of-bound track index (e.g. -1) is equivalent to
  disabling a renderer prior to the generalization.
- A prepared TrackRenderer that exposes 0 tracks is equivalent to a
  TrackRenderer in the STATE_IGNORE state prior to the generalization.

Issue #514.

This will allow multi-track support when consuming from a SampleSource to
be added in a single class, rather than in 6. Prep for Issue #514.

On NVIDIA Shield, recreated passthrough AudioTracks have incorrect playback head
positions, due to shared state with the previously destroyed passthrough
AudioTrack. Calling AudioTrack.flush() before AudioTrack.release() ensures this
state is cleared.

This is a safe change so I have not made it a device-specific workaround. The
combined time for flush and release is less than 10 ms (with flush normally
taking less than two ms).

- Also avoid boxing when passing the seek position to the background
  thread.

Issue: #654

Fix crash on screen touch before starting playback. mediaController cannot be
used until after setMediaPlayer has been called on it.

See H.265/HEVC specification subsection 7.3.4.

Issue #464
Issue #665

Issue: #672

Everything I've seen that uses ExoPlayer sets it to true, and
setting it to false is poorly supported / likely to result in
bad initial A/V sync after each seek.

Issue: #662

Issue: #587