• homepage: http://ffmpeg.org/
• github: https://github.com/FFmpeg/FFmpeg

Split audio from video

ffmpeg -i video.mp4 output_audio.wav

http://superuser.com/questions/609740/extracting-wav-from-mp4-while-preserving-the-highest-possible-quality

Merge audio to a video

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -strict experimental output.mp4

http://superuser.com/questions/277642/how-to-merge-audio-and-video-file-in-ffmpeg

Compress MP4

ffmpeg -i video.mp4 -vcodec h264 -b:v 1000k -acodec mp2 output.mp4