avcodec/videotoolboxenc: Fix concurrent access to CVPixelBufferRef

For a frame comes from AV_HWDEVICE_TYPE_VIDEOTOOLBOX, it's
CVPixelBufferRef is maintained by a pool. CVPixelBufferRef returned
to the pool when frame buffer reference reached to zero. However,
VTCompressionSessionEncodeFrame also hold a reference to the
CVPixelBufferRef. So a new frame get from av_hwframe_get_buffer
may access a CVPixelBufferRef which still used by the encoder.
It's only after vtenc_output_callback that we can make sure
CVPixelBufferRef has been released by the encoder.

The issue can be tested with sample from trac #10884.
ffmpeg -hwaccel videotoolbox \
	-hwaccel_output_format videotoolbox_vld \
        -i input.mp4 \
	-c:v hevc_videotoolbox \
	-profile:v main \
        -b:v 3M \
        -vf scale_vt=w=iw/2:h=ih/2:color_matrix=bt709:color_primaries=bt709:color_transfer=bt709 \
        -c:a copy \
	-tag:v hvc1 \
	output.mp4

Withtout the patch, there are some out of order images in output.mp4.

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>

0 files changed, 0 insertions, 0 deletions