AVHWAccel.end_frame can run on a worker thread. The assumption of the
frame threading code is that the worker thread will change the AVFrame
image data, not the AVFrame fields. So the AVFrame fields are not synced
back to the main thread. But this breaks videotoolbox due to its special
requirements (everything else is fine). It actually wants to update
AVFrame fields.
The actual videotoolbox frame is now stored in the dummy AVBufferRef, so
it mimics what happens in non-videotoolbox cases. (Changing the
AVBufferRef contents is a bit like changing the image data.) The
post_process callback copies that reference to the proper AVFrame field.
Based on a patch by wm4.
Signed-off-by: Aman Gupta <aman@tmm1.net>
Previously the codec kept an entire copy of the SPS, and restarted the VT decoder
session whenever it changed. This fixed decoding errors in [1], as
described in 9519983c. On further inspection, that sample features an SPS change
from High/4.0 to High/3.2 while moving from one scene to another.
Yesterday I received [2], which contains minor SPS changes where the
profile and level do not change. These occur frequently and are not associated with
scene changes. After 9519983c, the VT decoder session is recreated unnecessarily when
these are encountered causing visual glitches.
This commit simplifies the state kept in the VTContext to include just the first three
bytes of the SPS, containing the profile and level details. This is populated initially
when the VT decoder session is created, and used to detect changes and force a restart.
This means minor SPS changes are fed directly into the existing decoder, whereas
profile/level changes force the decoder session to be recreated with the new parameters.
After this commit, both samples [1] and [2] playback as expected.
[1] https://s3.amazonaws.com/tmm1/videotoolbox/spschange.ts
[2] https://s3.amazonaws.com/tmm1/videotoolbox/spschange2.ts
Signed-off-by: Aman Gupta <aman@tmm1.net>
This fixes decoding of H264 video samples with SPS and PPS changes.
See for example https://s3.amazonaws.com/tmm1/videotoolbox/spschange.ts,
which previously stalled the decoder and failed to produce any new frames
after the SPS change.
Also see https://s3.amazonaws.com/tmm1/videotoolbox/ppschange.ts, which
uses multiple PPS and would previously cause VT decode failures.
If the VideoToolbox session needs to be restarted, and
videotoolbox_start() fails for some reason (for instance, if the video
is interlaced and the decoder is running on iOS), avcodec will return
AVERROR_EXTERNAL. This can be used by the API user to switch to another
decoder.
Signed-off-by: Aman Gupta <aman@tmm1.net>
