CUDA/CUVID decoding error

[lasereyess]

Apologies if this isn't filled out properly, my version of ffmpeg is not listed and I don't know what component this falls under (codecs I think?).

When decoding files with CUDA on mpv I get some garbage lines on the bottom, I have only been able to reproduce it with a single file, so it may be an issue with the aspect ratio of the file? I'm not sure.

With ffmpeg I can reproduce by decoding with CUDA to an image

% ffmpeg -c:v h264_cuvid -ss 00:00:10.0 -i test.mkv -vframes 1 output.png

with mpv (I know this isn't useful to you guys but it's how I discovered this bug) it can be reproduced using:

mpv --hwdec=cuda --no-config test.mkv 

ffmpeg version:

ffmpeg version 3.3.3 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 7.1.1 (GCC) 20170630
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avisynth --enable-avresample --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libass --enable-libbluray --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxvid --enable-shared --enable-version3
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libavresample   3.  5.  0 /  3.  5.  0
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100

OS: GNU/Linux 64 bit
GPU: Nvidia GTX 960

[lasereyess]

example of decoding issues

[lasereyess]

file in question that produces garbage decoding

[Timo R.]

Please provide the full ffmpeg output.
And the sample you used to create this behavior.

Right now I suspect it's an error in the file, where it might be missing cropping information.
But it's impossible to tell without those things.

Does it work fine when software decoded?

[lasereyess]

Log file is now attached.The sample used to create that image is also attached. LB-test-small.mkv. Specifically I reran the command with

ffmpeg -report -c:v h264_cuvid -ss 00:00:01.0 -i LB-test-small.mkv -vframes 1 output.png

and it indeed produces the same output.png with the green line at the bottom.

It plays back fine using vdpau as well as software decoding.

[lasereyess]

logfile

[Timo R.]

Yeah, same thing is happening here.
Not sure what causes it yet.

[lasereyess]

Is there any more information that could be useful that I can give?

[Philip Langdale]

It'll either be a driver bug or some incompatibility with some hardware constraint (and nvidia do a poor job of documenting the hardware constraints and capabilities around nvdec). My first thought was the 534 vertical resolution but this was correctly padded out to 544 in your sample when encoding, so that shouldn't be a problem.

[Philip Langdale]

(And for what it's worth, I was able to reproduce with your sample)

[lasereyess]

FWIW I'm using the latest nvidia drivers for linux and my GPU is 'rev a1' (no idea if this is relevant)

NVRM version: NVIDIA UNIX x86_64 Kernel Module  384.59  Wed Jul 19 23:53:34 PDT 2017
01:00.0 VGA compatible controller: NVIDIA Corporation GM206 [GeForce GTX 960] (rev a1)

Is it worth trying to report this as a bug to nvidia? Do they take bug reports like this? If they take them, do they care about them at all?

[Philip Langdale]

They sometimes care about it. You can report on their forums:

​https://devtalk.nvidia.com/default/board/175/video-technologies/

[Balling]

Working for me. (1280 x 534 all pixels are black, though checked only in windows, everything it the last version). Checked both:

ffmpeg.exe -hwaccel nvdec -ss 00:00:10.0 -i LB-test-small.mkv -vframes 1 output.png
ffmpeg.exe -c:v h264_cuvid -ss 00:00:10.0 -i LB-test-small.mkv -vframes 1 output.png