SDK / exoplayer

This is useful to allow playback of individual segments from a
DASH stream as regular fmp4 files. These segments don't typically
contain a segment index. For playback to start, we need to invoke
seekMap with the UNSEEKABLE index. We do this if we haven't seen
a segment index when we encounter an mdat box (if one were present,
it would have been located earlier than this point).

If the manifest server response arrived after the player was released, the
renderer builder would set up renderers for a released player, causing an
exception to the thrown in the DASH case.

Also fix Issue #657

Issue: #641

Issue #641

1. [Cleanup] Remove unused Track types, including TYPE_TIME_CODE.
2. Add subtitle track type, which is different to the existing text type.
3. Set duration on the media formats for text and subtitle tracks. This
   was causing the player to report unknown media duration for mp4 files
   containing such tracks.
4. Make TextTrackRenderer do the right thing when not started.

Issue: #635

- Make UnrecognizedInputFormatException public so the app can more easily handle
  it when it is propagated to onPlayerError.
- Format the description using the simple class names for the extractors.
- Don't retry loading after it's thrown, but just throw immediately.

Issue: #641

Add support for HEVC video in Matroska files

add support s263

- ExtractorSampleSource takes an array of extractors to test for suitability.
- Extractors now implement a sniff() method that returns whether they can
  extract samples in the input stream's format.
- Switch demo app samples to use format detection.

Issue: #438

Issue: #599

1. Fix seeking in test2.mkv by handling non-default timescale
   after duration.
2. Fix handling of missing cues in test6.mkv by allowing playback
   to continue (but all seeks will reset to t=0).

Issue #631

Issue: #595

GitHub issue: #589

Issue: #589