[FFmpeg-devel] [PATCH] libavcodec/videotoolbox: let VideoToolbox choose a decoder for us

[王 氚]

Just dig it a little bit, and I found that the first attempt of [VTDecompressionSessionCreate] is always ok, if we try to decode some normal size of video(for example, 640x480, 1280x720...)

But it will fail, it we try to decode h264 video with some special size(for example, 300x180).

So it seems like there are some limitations in [VTDecompressionSessionCreate], but if we give VideoToolbox freedom to choose a decoder,  it's always OK.

And I try to find some information about this, but there isn’t so many detail information about this in apple’s document:(

Any suggestions?
On Aug 2, 2020, 1:11 AM +0800, Hendrik Leppkes <h.leppkes at gmail.com>, wrote:
> On Sat, Aug 1, 2020 at 6:25 PM 王 氚 <ouchuanm at outlook.com> wrote:
> >
> > I’m just looking at the bug https://trac.ffmpeg.org/ticket/8789
> > And I found that in this case, VTDecompressionSessionCreate will fail and return kVTVideoDecoderNotAvailableNowErr
> >
> > While according to the document of [VTDecompressionSessionCreate], it is possible to give a null
> > And let videotoolbox to choose a decoder.
> > https://developer.apple.com/documentation/videotoolbox/1536134-vtdecompressionsessioncreate?language=occ
> >
>
> Can you explain under what circumstances this might occur, and why the
> second try would work?
> And once we know that, can't we just improve the first attempt?
>
> - Hendrik
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