FFmpeg commands

To convert an MKV to MP4:

C:\Program Files\WinFF\ffmpeg.exe -i input.mkv -c copy output.mp4

To extract the audio from an MP4:

C:\Program Files\WinFF\ffmpeg.exe -i use-audio.mp4 -vn -acodec copy audio.mp4

To replace the audio in an MP4:

C:\Program Files\WinFF\ffmpeg.exe -i use-video.mp4 -i audio.mp4 -vcodec copy -acodec copy -map 0:0 -map 1:0 output.mp4