How do I replace the audio in an MP4 file without re-encoding?

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Full question
https://superuser.com/questions/602662/h...

Question links:
[add another audio stream to]: https://superuser.com/questions/53782/ho...
[convert the audio format of]: https://superuser.com/questions/331717/h...
[Journeyman Geek suggested in chat]: http://chat.stackexchange.com/transcript...

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Tags
#windows #audio #mp4 #videoencoding

#avk47

ACCEPTED ANSWER

I ended up scrutinizing the documentation for ffmpeg and worked out a solution:

ffmpeg.exe -i input_video.mp4 -i replacement_audio.m4a -vcodec copy -acodec copy -map 0:0 -map 1:0 output.mp4

An addition to the current solution: If the audio file does not match the video container's format, just avoid the -acodec parameter:

ffmpeg.exe -i input_video.mp4 -i replacement_audio.m4a -vcodec copy -map 0:0 -map 1:0 output.mp4

Now, only the audio gets encoded in order to match the container.

There are several free software for this:

and many others at videohelp.com

I'm surprised that no one mentioned onlineconverter.com. In addition to many other goodies, their site allows to add or replace audio in a video file.

Trying it out, replacing the audio in a sample video file does not seem to affect the video.