ffmpeg audio mux delay

ffmpeg can be used to mux different video and audio sources, even making audio delay.

$ ffmpeg -i input_0.mp4 -i input_1.mp4 -c copy -map 0:v:0 -map 1:a:0 -shortest out.mp4

REF: http://stackoverflow.com/questions/12938581/ffmpeg-mux-video-and-audio-from-another-video-mapping-issue