ffmpeg -i <<video>> -vf "select=eq(pict_type\,I)" -vsync vfr frame_%04d.png -hide_banner
ffmpeg -i input.mkv -codec copy output.mp4
Source: Ask Ubuntu topic
ffmpeg -i <<video>> -vf "select=eq(pict_type\,I)" -vsync vfr frame_%04d.png -hide_banner
ffmpeg -i input.mkv -codec copy output.mp4
Source: Ask Ubuntu topic