This blog post will explain how to split a video into a seperate video and audio stream with FFMPEG. The file infile.mp4 will be used as the input file. The -an -c:v copy flags will copy the video stream into videoout.mp4. The -vn -c:a copy flags will copy the audio stream into audioout.mp4. The audio and video streams are encoded as mp4 files.

ffmpeg -i infile.mp4 -an -c:v copy videoout.mp4 -vn -c:a copy audioout.mp4