dahua

ffmpeg -y -i file.dav -vcodec libx264 -crf 24 file.mp4

https://gist.github.com/jdye64/ca07e01ff3d8e93210c3

para converter todos os ficheiros numa pasta:
for i in *.dav; do ffmpeg -y -i "$i" -vcodec libx264 -crf 24 "${i%.*}.mp4"; done

https://stackoverflow.com/a/33766147

ou talvez melhor:
for i in *.dav; do ffmpeg -y -i "$i" -c:v libx265 -crf 26 -preset fast "${i%.*}.mp4"; done