Fails to build with ffmpeg 8

[lfos]

🐛 Describe the bug

Attempting to rebuild our torchvision packages at Arch Linux against ffmpeg 8 fails with:

/build/torchvision/src/python-vision-0.23.0/torchvision/csrc/io/decoder/video_stream.cpp: In member function ‘virtual void ffmpeg::VideoStream::setHeader(ffmpeg::DecoderHea
der*, bool)’:
/build/torchvision/src/python-vision-0.23.0/torchvision/csrc/io/decoder/video_stream.cpp:125:32: error: ‘AVFrame’ {aka ‘struct AVFrame’} has no member named ‘key_frame’
  125 |     header->keyFrame = frame_->key_frame;
      |                                ^~~~~~~~~

Versions

0.23.0 but does not seemed to be fixed on master either

[lfos]

From what I can tell, this doesn't seem to be addressed by the pending PR #9231.

[NicolasHug]

Hi @lfos , we have deprecated the torchvision C++ decoder part, and from 0.24 which we'll release in a few weeks, it will stop being built by default.

[lfos]

@NicolasHug - Thanks for the update! As it's still a few weeks, is there any change we can cherry-pick, so 0.23.0 can be built against ffmpeg 8? For context, torchvision is one of the last remaining packages blocking our ffmpeg 8 rebuild at Arch Linux.

[1] https://archlinux.org/todo/ffmpeg-80-and-friends/

[lfos]

FWIW, the following patch seems to fix the build:

--- a/torchvision/csrc/io/decoder/video_stream.cpp	2025-09-29 09:28:57.678370404 -0400
+++ b/torchvision/csrc/io/decoder/video_stream.cpp	2025-09-29 09:29:51.544541164 -0400
@@ -122,7 +122,7 @@ int VideoStream::copyFrameBytes(ByteStor
 void VideoStream::setHeader(DecoderHeader* header, bool flush) {
   Stream::setHeader(header, flush);
   if (!flush) { // no frames for video flush
-    header->keyFrame = frame_->key_frame;
+    header->keyFrame = !!(frame_->flags & AV_FRAME_FLAG_KEY);
     header->fps = av_q2d(av_guess_frame_rate(
         inputCtx_, inputCtx_->streams[format_.stream], nullptr));
   }