videotoolboxenc: h264_videotoolbox is not writing b-frames

[Nomis101]

hevc_videotoolbox does write b-frames, but h264_videotoolbox does not.

Steps:

1. Encode a video with h264_videotoolbox

$ ffmpeg -i input.foo -acodec copy -vcodec h264_videotoolbox -b:v 20000k -profile:v main /ffmpeg_output.mp4

2. check the video for b-frames

$ ffprobe -show_frames ffmpeg_output.mp4 > outputfile.txt

In outputfile.txt there is pict_type=P and pict_type=I only, there is no pict_type=B

Full output is attached.

[Nomis101]

Full output

[Balling]

Really?

[Nomis101]

HandBrake uses a patch to fix this
​https://github.com/HandBrake/HandBrake/blob/master/contrib/ffmpeg/A04-videotoolbox.patch

[Balling]

Was partially fixed here 5e0a3278bb7385f9fee158ccd69b07bf76a9e5df and you need to add

vtctx->has_b_frames = avctx->max_b_frames > 0;

after ​https://github.com/FFmpeg/FFmpeg/blob/55755b4ab27a94bfa1d91e494441dc2168164d19/libavcodec/videotoolboxenc.c#L1357 in else.

[Nomis101]

Thanks, I will try to make a commit according to your suggestions.

[Balling]

Replying to Nomis101:

Thanks, I will try to make a commit according to your suggestions.

On the second thought dunno how it will fix the issue, after all it is in else of if check for AV_CODEC_ID_H264... heh.

But still please submit it...

[Balling]

​https://patchwork.ffmpeg.org/project/ffmpeg/patch/20200229013951.7792-1-Nomis101@web.de/ maybe you will review it? Though it does not look like it will solve the issue.

[Rick Kern]

Use the -bf parameter to something non-zero to enable B-frames for H.264. If the hardware doesn't support B-frames however, they won't be written.