user6038: I have two files, one is MP4 file with video only and another is M4A audio file. What is the best and simpliest method of merging these two tracks in a single MP4 container? Is it possible to do this without transcoding (loosing quality)? Thanks!
Open source and free software is my preference.

user3295: MP4muxer will do the job, it even takes raw h264 streams.
This process is usually called "muxing" and can be done with virtually any container format.
Of course audio and video has to have the exact same length to have synchronized audio and video.

user16561: ffmpeg looks promising. Might be worth a shot.
Specifically, the command
ffmpeg -i video.mp4 -i audio.m4a -acodec copy -vcodec copy output.mp4

should do the trick.

6038: <p>I have two files, one is <strong>MP4</strong> file with video only and another is <strong>M4A</strong> audio file. What is the best and simpliest method of merging these two tracks in a single MP4 container? Is it possible to do this without transcoding (loosing quality)? Thanks!</p>

<p>Open source and free software is my preference.</p>
 3295: <p><a href="http://www.videohelp.com/tools/MP4Muxer" rel="nofollow">MP4muxer</a> will do the job, it even takes raw h264 streams.</p>

<p>This process is usually called "muxing" and can be done with virtually any container format.
Of course audio and video has to have the exact same length to have synchronized audio and video.</p>
 16561: <p><a href="http://www.ffmpeg.org/download.html" rel="noreferrer">ffmpeg</a> looks promising. Might be worth a shot.</p>

<p>Specifically, the <a href="https://www.youtube.com/watch?v=eXfp4S1xZsw" rel="noreferrer">command</a></p>

<pre><code>ffmpeg -i video.mp4 -i audio.m4a -acodec copy -vcodec copy output.mp4
</code></pre>

<p>should do the trick.</p>
