[Bug 99029] VCE VAAPI segfault using ffmpeg

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99029

--- Comment #6 from Andy Furniss <adf.lists at gmail.com> ---
(In reply to Martin Bednar from comment #4)
> The file is the OSS Elephant's dream movie : https://orange.blender.org/
> Purposely tested with this for easy sharing.
> Contained streams (ffmpeg -i ): 
>     Stream #0:0: Video: msmpeg4v2 (MP42 / 0x3234504D), yuv420p, 1920x1080,
> 10002 kb/s, 24 fps, 24 tbr, 24 tbn, 24 tbc
>     Stream #0:1: Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, 5.1(side),
> fltp, 448 kb/s

I think ffmpeg will silently fall back to s/w decode with this file as it's not
normal h264.

If you don't specify a bitrate it seems ffmpeg will use cqp = 20 (which will
come out quite high bitrate on some content).

> -profile:v 77  : I tested values and in the end found one in ffmpeg sources.
> Are these values documented anywhere?

Not sure about ffmpeg, but they are standard numbers in the world of h264

> B-Frames : so basically VCE is useless in its B-Frame-less state?

I wouldn't go that far, for realtime encoding it is useful and libx264 with
realtime settings wouldn't use b-frames either (well depends on how much CPU
you have available in practice).
For example my card can do 2160p60 realtime in an artificial test - though in
practice for say, game/screen recording I would need hardware CSC which Windows
may have, but linux doesn't.

> I was hoping to create a tvheadend streaming server with live hw-accelerated
> transcoding, is this at all possible with AMD VCE cards?

If the input is progressive h.264 maybe - VCE doesn't encode interlaced which
could be an issue depending on what your local broadcasters use.

TV tends to be quite low bitrate anyway - if you are not reducing size then
re-encoding may not be the best way to go.

gstreamer can, for my dual instance VCE card, be faster than ffmpeg, on your
APU I don't know whether it would be.

gstreamer can use vaapi (I don't think a current mesa regression affects
transcoding). OMX can be used, but it's cqp only, with vaapi you can target
bitrates.

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