Convert Mp4 (AAC) to MP4 (AC3)

[GreaterMuta]

I know that i can extract the streams from the MP4, covert the audio and then create another MP4 from those streams. But i was wonderign if there is a way to do this in a more automated fashion. Such as a command for ffmpeg that i could maybe run as a batch command? The problem i have is that i have many MP4s that i need to do this with, so doing each one manually is an extremely time consuming process.

[racer-x]

Bad idea.....

Mp4 should use aac not ac3.

[Baldrick]

See https://forum.videohelp.com/threads/356314-How-to-batch-convert-multiplex-any-files-with-ffmpeg

and the batch something like

for %%a in ("*.mp4") do ffmpeg -i "%%a" -c:v copy -c:a ac3 -b:a 224k "newfiles\%%~na.mp4"
pause

224k is the audio bitrate.

But why do you need ac3?

[GreaterMuta]

Bad idea.....

Mp4 should use aac not ac3.

The files won't be staying as MP4, they will be converted to blu rays. The reason for needing the change in audio is due to a problem i found occuring over and over. When trying to author a blu from the MP4 files as is, i always end up with audio sync issues. I did however find a work around for this. Which is to extract tge streams, convert the audio and the create an MP4 again. That MP4 when converted to blu has no audio sync issue.