[FFmpeg-user] Problem editing m4a files with ffmpeg

richard richard at richsim900.plus.com
Fri May 20 15:43:41 CEST 2011

When I edit an m4a file using ffmpeg using command like this:

ffmpeg -i filename.m4a -ss 00:02:34 -t 00:28:35 -acodec copy

the edited file will play OK on software media players, but large m4a
files won't play on my Marantz CD6003. The files timeout after 30

If I use mp4creator to optimize the edited m4a file using command like

mp4creator -optimize filename.m4a

the optimized file plays OK on the Marantz. 

I found out using AtomicParsley that editing an m4a file with ffmpeg
moves the mdat atoms from the end of the file to near the front. This
seems to be an issue for the Marantz. mp4creator moves the mdat atoms
back to the end of the file again.

Is this a bug in ffmpeg?

You kindly fixed another issue with the Marantz here:-


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