Combine sound such as MP3 to video MOV in OS X?
ffmpeg supports combining video and audio without re-encoding:

ffmpeg -i input.mov -i input.mp3 -c copy -map 0:0 -map 1:0 -shortest output.mov


-map 0:0 means input file 0, stream 0. -c copy copies video and audio codecs. -shortest makes the combined file as long as the shorter file.