PlaybackManager's ref counting was only used to keep it alive in a few
callbacks. Instead, the callbacks can use weak references that can only
be used from the thread that the PlaybackManager was created on, to
ensure that the PlaybackManager can't be destroyed while being
accessed.
This ensures that:
- The PlaybackManager is destroyed immediately when it is reassigned
by HTMLMediaElement
- No callbacks are invoked after that point
This fixes the crash initially being addressed by #8081. The test from
that PR has been included as a regression test.
In order to free up memory when a video is paused for an extended
period, we add a new Suspended state to PlaybackManager which tells the
data providers to suspend. The data providers will handle this signal
by disposing of their entire decoded data queue and flushing their
decoder.
When initially creating a PlaybackManager, and when resuming to a
paused state, the delay before suspension will be much lower than when
pausing from any other state. This is intended to prevent media
elements from consuming memory for long when decoding the first frame
for display, as well as to allow the data providers to suspend much
more quickly after a seek while paused.
Currently, resuming playback doesn't display much of a delay on my
MacBook, though that may change once we completely tear down the
decoder in the suspended state. It may also be exacerbated by using
hardware decoders due more complex decoder initialization.
`IncrementallyPopulatedStream::Cursor` now tracks whether it's currently
blocked inside a wait for more bytes, allowing higher layers to
distinguish "no frames yet" from "decoder is idle".
Enter buffering when `DisplayingVideoSink` runs out of frames and the
associated `VideoDataProvider` is blocked waiting for data to arrive.
Exit buffering once decoding refills the frame queue.
For now, buffering behaves like paused, but it gives us an explicit
state to hook UI into.
For some reason, it seems that passing NonnullRefPtr<SeekData> const&
was causing us to triple ref() in the capture group for the audio seek
handlers, followed by only a single unref(). Changing this to plain old
SeekData& inexplicably fixes the leak.
When accurate seeking, we can assume that the chosen timestamp will be
the seek's target timestamp. Therefore, we can run the audio seeks
simultaneously with the video seeks to allow them to finish (probably)
before the video seeks themselves complete, making seeking slightly
more responsive.
This implementation allows:
- Accurate seeking to an exact timestamp
- Seeking to the keyframe before a timestamp
- Seeking to the keyframe after a timestamp
These three options will be used to satisfy the playback position
selection in the media element's seeking steps.
