SDK / exoplayer

This change removes the need for SourceBuilders to load their
manifests before building their sources. This is done by pushing
initial manifest loads into the ChunkSource classes. This simplifies
the SourceBuilders a lot, and also DemoPlayer.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=113259259

Notes:
1. The logic in ExoPlayerImplInternal is very temporary, until we
   have proper TrackSelector implementations. Ignore the fact that
   it's crazy and has loads of nesting.
2. This change removes all capabilities checking. TrackRenderer
   implementations will be updated to perform these checks in a
   subsequent CL.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=113151233

Move binding of tracks<->renderers to ExoPlayerImplInternal.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=113046018

GitHub note - Apologies for the cryptic change descriptions,
they relate to a design doc that's not externally visible.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=113043764

Fixes: #1176
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112781092

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112776882

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112774678

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112736771

When a seek is performed, renderers currently perform the
actions that they need to take in two places: Some changes
are performed in seekTo implementations. Other changes are
performed when discontinuities are read from the source.

In HLS we need to perform what is effectively a seek
originating in the source. To support this, this CL allows
discontinuities read from the source to modify the playback
position. All actions that renderers perform as a result
of a seek are moved to be performed when a discontinuity is
received.

Best way to understand CL:
- Look at SampleSource interface change and then at the
  concrete implementations, to make sure they've been
  changed properly.
- Look at SampleSourceTrackRenderer change.
- Look at concrete renderers. The general pattern is that
  code previously performed in seekTo and READ_DISCONTINUITY
  is merged into onDiscontinuity().

Note: This will be further untangled in V2.

Issue #676
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112720746

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112699916

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112699244

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112693523

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112691130

Based on AOSP's MP3Extractor.cpp and ID3.cpp.

Issue: #497
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112685664

As part of this change, Extractor.sniff may read/skip (not just peek) if it
returns true. This allows Extractors to avoid parsing the input a second time in
read.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112683272

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112676296

Also fix a couple of style nits.

Issue: #398
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112412961

This makes sense until we need to support seeking in the live window.

Issue: #676
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112402026

Also apply the workaround for the secure variant of OMX.SEC.avc.dec.
Note that it's not necessary to do the same for the RK decoder in
the method below, since that workaround is targeted at SDK_INT<=17
and secure decoders only came along in 18.

Issue: #603
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112395376

link track language attribute in Smoothstream parser

Also simplify the implementation slightly.

Also, use terminology from ATSC spec in Ac3Util comment.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112254908

After this change, AC-3 uses about 20 KB and DTS uses 49 KB.

For comparison, 'normal' PCM playbacks use by default (depending on the device
and input format) about 45 KB. For passthrough, the following buffer sizes were
used before this change:
- Nexus Player AC-3: 23 KB
- Nexus Player DTS: 25 KB
- NVIDIA Shield AC-3: 15 KB
- NVIDIA Shield DTS: 16 KB (caused underruns in some DTS-HD playbacks)
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112254836

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112252404