How convert mp4/mkv file with AAC audio to AC3?

[jfca283]

Hi
Some time ago i used a script to perform that task.
It didn't touch the video. It just changed the audio format. From AAC to AC3.
Now i'm watching MKV/MP4 files which have the audio in the AAC format. Format that my receiver doesn't decode.
So, what can i do?
Where do i find an updated version of the old AAC2AC3 script?
Thanks for your time and interest.

[shantiq]

jf do this with your mkv

 time ffmpeg -i inputvideowithaacaudio.mkv -c:v copy -c:a ac3  outputmkvwithac3audio.mkv

replace ffmpeg with avconv if you have not got ffmpeg

[jfca283]

The command you provide doesn't process the video, right?
The following line, should it work?
time ffmpeg -i inputvideowithaacaudio.mp4 -c:v copy -c:a ac3 outputmkvwithac3audio.mkv
Processing a mp4 file?

[SeijiSensei]

The command will copy the video stream and convert the audio stream and store the result in the Matroska container.

You don't need the "time" command at the beginning either. That just tells the OS to report how long the task took. ffmpeg will report that itself anyway.

[jfca283]

So, for mkv files with AAC audio, i just need to run this
time ffmpeg -i inputvideowithaacaudio.mkv -c:v copy -c:a ac3 outputmkvwithac3audio.mkv
And for mp4, the following
time ffmpeg -i inputvideowithaacaudio.mp4 -c:v copy -c:a ac3 outputmkvwithac3audio.mkv
Am i right?

[shantiq]

yes you are right ¡totalmente! the time thing is good to see how long it takes
good luck should be quick!


but your second line should read

 time ffmpeg -i inputvideowithaacaudio.mp4 -c:v copy -c:a ac3  outputvideowithac3audio.mp4

since you are keeping the same video -c:v copy = codec video copy is what this means

[jfca283]

Thanks!

[Yellow Pasque]

but your second line should read ... mp4

ffmpeg would still copy the video and encode audio to AC3. It would then mux them into a Matroska container (instead of MPEG4 container).
So it probably doesn't matter, unless the OP intends to play the video on a device/system that can't handle a Matroska container. I guess there could be some differences in the container (chapter markers, tag information), but ffmpeg is usually smart enough to copy those things from one container to another.