Add an audio file to and mkv video

I'm quite new to multimedia things, I'm trying to find a way to make nice screencasts, I've already been able to capture my desktop with ffmpeg:

$ ffmpeg -f alsa -ac 2 -i hw:0,0 -f x11grab -r 30 -s $(xwininfo -root | grep 'geometry' | awk '{print $2;}') -i :0.0 -acodec pcm_s16le -vcodec libx264 -vpre lossless_ultrafast -threads 0 -y out.mkv

It works pretty nice, but I'd like to add music in the background, if I add it with mencoder:

mencoder -ovc copy -oac mix -audiofile track.mp3 out.mkv -o out.mp4

It delete the video sound, I don't want to replace it, I want to add music to my explanation, any ideas?

3 Answers

You can install mkvtoolnix;

sudo apt-get install mkvtoolnix

Then use mkvmerge from the installation to mux audio and video into the mkv container from the command line.

There is also a Gui tool, mkvtoolnix-gui that is a front end to mkvtoolnix.

sudo apt-get install mkvtoolnix-gui

Example to mux video file called, input-video.mkv with a sound file called soundfile.mp3, creating a new muxed mkv file called output-with-sound.mkv, do the following in the directory where you have the video without audio and the audio file:

mkvmerge -o output-with-sound.mkv -A input-video.mkv soundfile.mp3

More examples including synchronization here:

kdenlive and add a second audio track, then remux

I'm not sure why mencoder didn't work for you, but you can also do the same thing with ffmpeg. You just need to use two inputs to ffmpeg.

 ffmpeg -i track.mp3 -i out.mkv -vcodec copy -acodec libfaac -ab 192k final.mkv

I didn't try it, but I don't think you can do -acodec copy, especially since you're using two different codecs. Just pick whatever you want in the output and add that in, its really fast compared to the video.