GitLab

A number of changes to improve AV sync at playback start:

- AvSync now will not perform corrections if it measures a slope that is
way off from what it expects. There are a number of reasons this could
happen:
  - Samples measured right after resuming playback may be from the
  paused state, which messes with the measured slope. This is especially
  important given our current interaction with the
  BufferingController...
  - Some vendor video decoder implementations will play video at an
  accelerated rate if they are not able to start playback in time, to
  'catch up' to the required value, and then resume normally. We need to
  ignore this behavior in AvSync.

- Modify the initialization of AvSync a bit to treat Start/Stop similar
to Pause/Resume. From the prespective of AvSync these should be
identical calls, and should maybe be combined to one in the future.
Also, due to the interaction with BufferingController, Start is actually
Start + Pause + Resume, so we need to treat Resume as we do for Start,
because the start of playback is actually the first Resume.

- For AvSync to compare the slope to an expected case, it needs to know
the current rate of playback, so add code from MediaPipelineBackend to
notify AvSync of playback rate changes.
  - As a bonus, the playback rate change is handled a bit better now.
  It's not perfect, but this is the first time I'm testing it as it
  seems no app supports it.

- Add ability for linear regression to dump its samples. This is very
useful for debugging unexpected slope calculations. This was very useful
to root cause the issue.

Bug: b/110481225
Test: Manual

Change-Id: I28ffa83c633446f2441ff5dfb8d5674b5e149ea5
Reviewed-on: https://chromium-review.googlesource.com/1132518Reviewed-by: Sergey Volk <servolk@chromium.org>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Commit-Queue: Mina Almasry <almasrymina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575130}