FFmpeg

Merging mp4 and m4a

Using ffmpeg you can combine the two together:

# ffmpeg -i video.mp4 -i audio.m4a -acodec copy -vcodec copy output.mp4

Extracting a video section

To extract a video section:

# ffmpeg -i input.mp4 -ss 00:00:15 -t 00:00:10 -async 1 output.mp4

Where:

-ss	The start time in HH:MM:SS
-t	The length of the video in HH:MM:SS

Issues

Copying DASH video (via -vcodec copy) using versions older than 0.10 will result in an empty file because it is unable to read the video contents.