[FFmpeg-devel] QSV Decoding - Issues and Regressions

[wm4]

On Mon, 3 Aug 2015 22:25:20 +0300
Ivan Uskov <ivan.uskov at nablet.com> wrote:

> Hello Michael, Hendrik,
> 
> I would like to make sure about following moment regarding handling of
> sequence header changing. The decoder has buffering of decoded frames,
> so when new frame dimensions are detected we can not just reset
> decoder, we should to deffer re-init and switch decoder  to some
> "flushing" state and still deliver "old" frames until buffer will
> empty.
> Main issue that upstream  still deliver new packets at this time. I
> tried to return 0 from ff_qsv_decode() to indicate that packet not
> consumed at all and should be re-send later but upstream does not
> understand this at least if  I return non-zero 'got_frame' flag and
> decoded frame. 

Video packets are always fully consumed. Yes, this can be a problem for
such APIs. But currently we don't have anything better. This was
extensively discussed, and the best fix would be a new API, which won't
happen within near time.

So you have to deal with this situation.

> Looks like decoder should to buffer income packets at at flushing
> state. Else decoder loses first gop after new sequence header detected.
> Is it acceptable way? Any other alternatives. By my private opinion it
> would be much better if upstream did not try to push new packet if 0
> was returned from decoder together with decoded frame.
> 
> By the way, about old implementation which "worked fine".
> It just did drop all buffered frames at decoder re-init on new
> sequence header, there is nice comment inside old qsvdec_h264.c:
> /* TODO: flush delayed frames on reinit */
> 
> Of course, I can provide same behavior for first time but it very ugly solution.

I was under the impression that the original Libav code handled this
correctly.

> 
> 
> Monday, August 3, 2015, 3:44:17 PM, you wrote:
> 
> [...]
> MN> thanks, ill leave qsv review & patch apply to you.
> MN> I had until recently not even a setup to build qsv as the stuff didnt
> MN> like my main development box. And still dont have a setup to runtime
> MN> test, just to build.

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