New subject: #10374(avcodec:closed): Problems to decode certain h264 keyframes with D3D11VA and DXVA2 hw acceleration

18 May 2023

      #10374: Problems to decode certain h264 keyframes with D3D11VA and DXVA2 hw
acceleration
-------------------------------------+-------------------------------------
             Reporter:  Florian      |                     Type:  defect
  Grill                              |
               Status:  new          |                 Priority:  normal
            Component:  avcodec      |                  Version:  6.0
             Keywords:  H264 dxva2   |               Blocked By:
  d3d11va                            |
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  1            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 I'm currently developing a streaming app for Windows and for my project I
 use the javacv project to use the native ffmpeg libraries
 [https://github.com/bytedeco/javacv]. Developing the first prototype was
 quite easy but upon further testing on different machines with different
 hardware decoders I noticed some strange effects with the D3D11VA and
 DXVA2 video decoder. It was just not possible to decode certain keyframes
 but cuvid or the software decoder had no problem to do so. On these
 problematic keyframes I always received an error when calling

 {{{
 final int err = avcodec_send_packet(this.m_VideoDecoderCtx, this.pkt);
 }}}

 The logs printed out ''"Invalid data found when processing input"'' but I
 was 100% sure that the data was correct so I started to dig into source
 code and did some research on the internet and I found the issue. It seems
 that in h264dec.h there is a variable called MAX_SLICES which is set to
 32.

 [https://github.com/FFmpeg/FFmpeg/blob/release/6.0/libavcodec/h264dec.h#L62]

 This MAX_SLICES value is used here dxva2_h264.c

 [https://github.com/FFmpeg/FFmpeg/blob/release/6.0/libavcodec/dxva2_h264.c#L4...]

 which leads to the fact that frames with larger slices simply can't be
 processed. This is strange limitation if you ask me.

 Other popular ffmpeg forks already increased this limit, e.g.

 [https://git.1f0.de/gitweb/?p=ffmpeg.git;a=commit;h=550cf548b546d386a6c634351...]

 In my example I used

 {{{
 this.m_VideoDecoderCtx.err_recognition(this.m_VideoDecoderCtx.err_recognition()
 | AV_EF_EXPLODE);
 }}}

 to get a proper error output but for testing I removed it and the frame
 that was processed and displayed looked like that

 [[Image(https://github.com/grill2010/ExampleDXVA2/blob/main/example_data/test.jpg)]]

 This behaviour can be easily reproduced with the latest ffmpeg version.
 The example h264 keyframe can be downloaded from here

 [https://github.com/grill2010/ExampleDXVA2/blob/main/example_data/example.h26...]

 How to reproduce:
 {{{
 % .\ffmpeg.exe -hwaccel dxva2 -i .\example.h264 test.jpg
 or
 % .\ffmpeg.exe -hwaccel d3d11va -i .\example.h264 test.jpg
 ffmpeg version 6.0 and latest SNAPSHOT
 built via https://www.gyan.dev/ffmpeg/builds/
 }}}

 On the ffmpeg version of javacv there was recently a patch for this small
 numbers of slices

 [https://github.com/bytedeco/javacpp-
 presets/commit/63acf680ef0d95cbdda1b3840450e4333a78bde0]

 and I can confirm that this fixes the issue completely (at least for
 D3D11VA). Btw. I found another ticket which might be related to this
 problem

 [https://trac.ffmpeg.org/ticket/9771]

 ----

 Like I said a fix was applied to the javacv ffmpeg version so I tried to
 compile this ffmpeg version for Windows x86_x64 with this increased
 MAX_SLICES for further testing. D3D11VA works perfectly fine now but I
 noticed another issue with DXVA2. Still on certain keyframes I received an
 error but this time a different one. When calling

 {{{
 final int err = avcodec_send_packet(this.m_VideoDecoderCtx, this.pkt);
 }}}

 I receive now

 {{{
 [h264 @ 0000027a270a1680] Buffer for type 5 was too small. size: 58752,
 dxva_size: 55296
 [h264 @ 0000027a270a1680] Failed to add bitstream or slice control buffer
 [h264 @ 0000027a270a1680] hardware accelerator failed to decode picture
 Error while decoding stream #0:0: Operation not permitted
 }}}

 Upon further investigation it turned out that the decoding of these
 certain keyframes fail because the buffer returned from the
 IDirectXVideoDecoder_GetBuffer function was too small. And I don't have
 any explanation why. DXVA2 works perfectly fine btw for h265 (not affected
 by the MAX_SLICES problem and not by the too small buffer problem).

 [https://github.com/FFmpeg/FFmpeg/blob/9d70e74d255dbe37af52b0efffc0f93fd7cb61...]

 I tested this behaviour now on 4 different PCs and the pattern I found is
 that it works on PCs with AMD or Intel GPUs but if you have an NVIDIA GPU
 you get this small buffer problem.

 How to reproduce:
 {{{
 % .\ffmpeg.exe -hwaccel dxva2 -i .\example.h264 test.jpg
 ffmpeg version with a patch which sets MAX_SLICES in dxva2_h264.c to 256
 built via javacv (java-presets build process)
 }}}

 I have provided here a Windows x64 ffmpeg build with that MAX_SLICES patch
 [https://github.com/grill2010/ExampleDXVA2/tree/main/example_data]

 ----

 I know that these are probably two bug reports in one but for me these
 things are related. The first problem with these small slices are probably
 an easy fix, the question is why is it like that in the first place? Other
 hw decoder for example like the dxva2 hevc decoder are overriding this
 small slice value but not dxva2 h264? Any reason for that? This is
 actually quite limiting the h264 hw acceleration for DXVA2 and D3D11VA.

 For the second problem with the too small buffer on DXVA2 I have
 absolutely no idea what could cause this issue and why it (seemingly) only
 occur on devices with an NVIDIA GPU. I would like to start some further
 testing but no idea where to start.

 I tried to provide as much details as possible if there are any questions
 just let me know.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10374>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker

#10374(avcodec:new): Problems to decode certain h264 keyframes with D3D11VA and DXVA2 hw acceleration

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