SDK / exoplayer

Improve WebVTT parser according to WebVTT spec

Prevent ArrayIndexOutOfBoundsException when proguard is enabled

- Line parameter
  - Added support for value and line alignment attributes.
  - Support negative numbers when line is an absolute number (not a
percentage).
- Position parameter
  - Added support for value and position alignment attributes
- Added support for WebVTT comment blocks
- Percentage values now accept decimal numbers (as webvtt spec states)
- Added new WebVTT tests for testing all new implemented features

Issue: #437

- do not denormalize styles at parsing time but only put normalized style info
into TtmlNode tree. Resolve styles on demand when Cues are requested for a
given timeUs.
- create TtmlRenderUtil to have static render functions separate
- added unit test for TtmlRenderUtil
- adjusted testing strategy for unit test to check resolved style on Spannables after rendering

Issue: #791

Issue: #789

There is no guarantee codec names start with this prefix in >= L.

Issue: #782

It can do weird things if the device has an unusual default Locale.
Util.toLowerInvariant uses the US Locale, which does the right thing
in this case.

- Allow a moof box to exceed the search size.
- Return immediately after reading an ftyp box with no compatible types.

Issue: #784

Partial fix for #778

This allows the demo app to display subtitles without video
(when there's no video, the shutter view does not hide itself).

When switching format in HLS, we instantiate a new extractor, which
adjusts TS presentation timestamps so that they align properly with
the start of the first segment in the new format. Some HLS streams
appear to have slightly misalignment that causes a glitch when using
this approach.

It's better to re-use the same timestamp adjustment across formats,
and only reset it when seeking or when there's an actual discontinuity.
This is because the HLS spec guarantees PTS timestamp alignment across
different formats.

We'll also need something like PtsTimestampAdjuster to share between
separated audio and WebVTT tracks, which also contain PTS timestamps
that are aligned, and will need to share a common adjustment.

Issue: #692

- Don't allow "nothing has changed" optimization in the case
  that only styling has changed (TextUtils.equals will return
  true in this case, but we shouldn't optimize).
- Add functionality to suppress embedded styling; seems useful
  to have.
- Added "this." for clarity.

Issue: #764

Issue: #707

Issue: #771

When a live stream ends, what typically happens is that the manifest
is refreshed and the refreshed version is not marked as live/dynamic.
When this happens we:

1. Don't want the duration of the track to change.
2. Still want to consider the possibility that we may have fallen behind
   the live window.
3. Don't want to allow futher manifest refreshes.

This change uses the right thing in the right place.

Issue: #707

Ignore extra returns in Subrip parsing

Issue #765

Issue #763

Issue: #755