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Extracting AAC-vbr from mpeg4 video

Hi

is there a way to extact a vbr aac-audio track from a mpeg4-video file? After using syntax:

ffmpeg -i infile.mp4 -map 0:x -acodec copy outfile.m4a (where x is audio track)

the extracted m4a-file shows cbr. How can I preseve vbr of the extracted audio? Any ideas welcome.

TIA.
lolly

Extracting AAC-vbr from mpeg4 video

Reply #1
How can you confirm the original audio track is vbr? By MediaInfo? Why does it matter?
If ffmpeg shows it is stream copy, then IMO it should be the original audio stream, no matter what MediaInfo tells.
I did a few test, right, ffmpeg created m4a file will always show as cbr in MediaInfo  , but there won't be any difference about audio streams. You can confirm by bit-compare using fb2k.

So, if you really care about MediaInfo, I would suggest you to use mp4box
Code: [Select]
mp4box -add "input.mp4#audio" "output.m4a"

Alternatively, you can simply remux your m4a through mp4box.

Extracting AAC-vbr from mpeg4 video

Reply #2
thanks huohok for your considerations. Indeed, I did analysis by MediaInfo. Will check out mp4box.

Extracting AAC-vbr from mpeg4 video

Reply #3
the extracted m4a-file shows cbr. How can I preseve vbr of the extracted audio? Any ideas welcome.

You do a raw copy, so no difference in your stream.
The detection of CBR/VBR in the MP4 file may be wrong.
I need the files (in and out) for patching that in MediaInfo.

Jérôme, developer of MediaInfo.

 
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