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

[Miroslav Slugeň]

Dne 13.2.2017 v 17:07 Philip Langdale napsal(a):
> 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
>
I am sure that i know what is going on, NVENC is inserting wrong SPS VUI 
aspect_ratio_idc to h264 packets when you encode at resolution 720x576 
and 720x480

AR 16:9 will insert aspect_ratio_idc=4 but it should be 
aspect_ratio_idc=255, sar_width=64, sar_height=45 for 720x576
AR 4:3 will insert aspect_ratio_idc=2 but it should be 
aspect_ratio_idc=255, sar_width=16, sar_height=15 for 720x576

MP4 and MKV containers contains correct AR metadata information which 
all players should accept, but TS container has nothing like that so it 
relies on what is inside h264 SPS.

Miroslav Slugeň
+420 724 825 885