How to remove a frame with ffmpeg without re-encoding?

Question

I am making a datamoshing program in C++, and I need to find a way to remove one frame from a video (specifically, the p-frame right after a sequence jump) without re-encoding the video. I am currently using h.264 but would like to be able to do this with VP9 and AV1 as well.

I have one way of going about it, but it doesn't work for one frustrating reason (mentioned later). I can turn the original video into two intermediate videos - one with just the i-frame before the sequence jump, and one with the p-frame that was two frames later. I then create a concat.txt file with the following contents:

file video.mkv
file video1.mkv

And run ffmpeg -y -f concat -i concat.txt -c copy output.mp4. This produces the expected output, although is of course not as efficient as I would like since it requires creating intermediate files and reading the .txt file from disk (performance is very important in this project).

But worse yet, I couldn't generate the intermediate videos with ffmpeg, I had to use avidemux. I tried all sorts of variations on ffmpeg -y -ss 00:00:00 -i video.mp4 -t 0.04 -codec copy video.mkv, but that command seems to really bug out with videos of length 1-2 frames - while it works for longer videos no problem. My best guess is that there is some internal checker to ensure the output video is not corrupt (which, unfortunately, is exactly what I want it to be!).

Maybe there's a way to do it this way that gets around that problem, or better yet, a more elegant solution to the problem in the first place.

Thanks!

Answer 1

If you know the PTS or data offset or packet index of the target frame, then you can use the noise bitstream filter. This is codec-agnostic.

ffmpeg -copyts -i input -c copy -enc_time_base -1 -bsf:v:0 noise=drop=eq(pos\,11291) out

This will drop the packet from the first video stream stored at offset 11291 in the input file. See other available variables at http://www.ffmpeg.org/ffmpeg-bitstream-filters.html#noise