Video encoding on Raspberry Pi 4 via ffmpeg and h264_v4l2m2m produces corrupted video

Question

• Raspberry Pi 4, 4 GB
• Rapsberry Pi OS Lite, 64 bit (2022-09-22)
• Kernel 5.15.61-v8+
• ffmpeg 4.3.4-0+deb11u1+rpt3

config.txt has the following relevant entry:

# Enable DRM VC4 V3D driver
dtoverlay=vc4-kms-v3d

According to my research, it would seem that the RPI4 is capable of hardware-accelerated video encoding using ffmpeg (from v4.3 on) via the h264_v4lm2m2 codec. ffmpeg -codecs and ffmpeg -encoders shows this codec to be available. Other people with a similar setup have gotten this to work successfully.

When I try this:

ffmpeg -i big_buck_bunny_720p_10mb.mp4 -c:v h264_v4l2m2m -c:a copy out.mp4

It gives me two warnings (see last two lines), but proceeds to encode the file anyway:

[h264_v4l2m2m @ 0x557353b190]  <<< v4l2_encode_init: fmt=0/-1
[h264_v4l2m2m @ 0x557353b190] Using device /dev/video11
[h264_v4l2m2m @ 0x557353b190] driver 'bcm2835-codec' on card 'bcm2835-codec-encode' in mplane mode
[h264_v4l2m2m @ 0x557353b190] requesting formats: output=YU12 capture=H264
[h264_v4l2m2m @ 0x557353b190] Failed to set number of B-frames: Invalid argument
[h264_v4l2m2m @ 0x557353b190] Failed to set gop size: Invalid argument

Hardware acceleration seems to work, as it encodes at ~130 fps. However, the resulting file is corrupted and can't be played.

What am I missing?

Answer 1

I eventually got this to work by swapping out the ffmpeg provided by apt and instead compiling the fork by jc-kynesim, which can be found at github.com/jc-kynesim/rpi-ffmpeg.

With this, it works, although I still get the following warning/ error:

[h264_v4l2m2m @ 0x556ff3d430] Failed to set gop size: Invalid argument

The encoding was a bit slower than before, clocking in at ~100 fps.

I don't know if the reason this fixed the problem is because this version of ffmpeg contains patches that solve the underlying problem, or if installing the numerous packages required for compilation actually brought in additional dependencies that were missing before. I've created an issue report on GitHub.