imx-vpu-hantro: broken A/V sync with VP8 playback


Carlos Rafael Giani
 

I recently noticed that VP8 playback does not work correctly with imx-vpu-hantro . If a VP8 stream contains alternate reference (altref) frames, then imx-vpu-hantro decodes them correctly, but does not inform about the fact that they are altref frames. This is a problem, because altref frames are supposed to be decoded, and NOT shown. In particular, timestamps should not be increased because of a decoded altref frame. They essentially are for internal use only.

However, because the callers do not know that a frame is an altref one, they don't skip them like they should. As a result, A/V sync gradually gets worse over time.

Is there any newer imx-vpu-hantro version that fixes this? The necessary fields are already there. Specifically, there's isGoldenOrAlternate in the FRAME struct in openmax_il/source/decoder/codec.h . However, it is never set to TRUE . I did some digging, and the only part that sets any flag like that is in vp8decmcapi.c (which is not used), and even then, this concerns itself only with golden frames, not altref ones.

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