[FFmpeg-user] What is a bitstream filter?

Nicolas George nicolas.george at normalesup.org
Wed Dec 5 15:30:45 CET 2012

Le quintidi 15 frimaire, an CCXXI, Arjun Krishnan a écrit :
> [mp4 @ 0x2bd10c0] malformated aac bitstream, use -absf aac_adtstoasc

Clearly, you read this error message.

> So I can get it to work if
> 1) Reencode it using -c:a libfaac, but this results in a lower bitrate, for
> some reason.
> ffmpeg -v verbose -i in.aac -acodec copy -c:a libfaac out.mp4

Well, for some reason you did not specify any bitrate or quality level, what
do you expect?

> 1) Can someone explain what's going on here?

AAC is not stored the same way in raw streams and in MP4 containers. That is
IMHO a pretty stupid design, but a lot of things work like that in the
MPEG-4 world.

Therefore, you can not just copy packets from a raw stream to an MP4

> 2) What is a bitstream filter? I cannot seem to find any useful information
> about.

A bitstream filter is a filter that works with encoded packets (the
"bitstream") rather than with decoded video frames or audio samples like the
filters in libavfilter.


  Nicolas George
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