[FFmpeg-devel] [PATCH] (for discussion): nvenc: fix wrong aspect ratio for 720x576 and 720x480 resolution

[Philip Langdale]

On Mon, 13 Feb 2017 07:21:51 -0800
Philip Langdale <philipl at overt.org> wrote:

> On Mon, 13 Feb 2017 08:52:34 +0100
> Miroslav Slugeň <thunder.m at email.cz> wrote:
> 
> > >    
> > I am using current STABLE drivers 375.26, because BETA drivers
> > 378.09 caused some crashes while encoding on NVENC.
> > 
> > I tested this on BETA drivers too and it is still same.
> > 
> > Original workaround is not working anymore :(
> > 
> > INPUT: Stream #0:0[0x401]: Video: mpeg2video (Main) ([2][0][0][0] / 
> > 0x0002), yuv420p(tv, top first), 720x576 [SAR 64:45 DAR 16:9], 25
> > fps, 25 tbr, 90k tbn, 50 tbc
> > 
> > OUTPUT: Stream #0:0[0x100]: Video: h264 (Main) ([27][0][0][0] /
> > 0x001B), yuv420p(progressive), 720x576 [SAR 16:11 DAR 20:11], 25
> > fps, 25 tbr, 90k tbn, 50 tbc
> > 
> > COMMAND: ffmpeg -deint adaptive -hwaccel cuvid -c:v mpeg2_cuvid -i 
> > "in.ts" -y -c:v h264_nvenc -c:a copy -b:v 1M -preset hq -f mpegts
> > "out.ts"
> > 
> > Also someone else is complaining about this issue: 
> > http://superuser.com/questions/1174097/ffmpegnvenc-encoding-strange-aspect-ratio
> > 
> > M.
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel at ffmpeg.org
> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel  
> 
> Can you point me to a sample that you see this behaviour with? I
> cannot reproduce with DVD sources here, which is where I saw the
> original problem.

You sent me a sample and I tried it out. I was able to reproduce your
problem, but it is not the original problem, and I wonder what is
really going on.

If you take your sample and your command line and then output to a
different container (i tried mkv and mp4), it's all correct - and it
would not be correct if my original workaround was still required.
There's something specific about using mpegts that leads to this
problem.

I'm not familiar with what parts of what metadata get respected in
different contextx For example, the out.ts, this command line produces,
is reported as having the right aspect ratio by mediainfo, but the
wrong one by ffprobe (and then plays back wrong, obviously).

Modifying the darWidth and darHeight leads to changes that are visible
in mediainfo, and are cumulative with respect to whatever bug is
hitting you here.

So, theory - there was a bug where nvenc was distorting the DAR and
that bug is now fixed. It seems like there is now some other bug, or
perhaps there always was a bug, which is modifying the SAR. Perhaps it
is doing it all the time but in other containers, container level
metadata is overriding it so it never becomes an issue.

Sounds like a great time for an nvidia dev to chime in :-)

--phil