[libav-tools] AAC encoded files show "0 kbps" average bitrate.

Luca Barbato lu_zero at gentoo.org
Mon Oct 8 22:27:33 CEST 2012


On 10/8/12 9:25 PM, Oliver Hookins wrote:
> Didn't get a chance to try this unfortunately, but I ended up
> re-encoding the files with the "-movflags frag_keyframe" option and
> the progressive-download playback problems went away. It's a bit odd
> because the container is MP4 and not MOV, and I understand this option
> to be more relating to video but evidently something in the code path
> is making a difference...


mp4 and mov are generated by the same muxer (and are the same format for 
the most part...)

>> So either flash is out of specification or there is something with the
>> specific player... (or the interpretation of the paragraph could be
>> different)
>
> Well, I'm encoding these with "-b:a 96000" and I would expect constant
> bitrate to be used, so this makes no sense on two levels. Given what I
> discovered above with the keyframe fragment option, the average
> bitrate metadata seems to be a red herring, but even obeying the
> standard, avconv should be setting a constant bitrate and expressing
> that bitrate in the metadata.

Apparently it isn't constant for the muxer check, looks like something 
is going on there...

Which is your exact command line ?

> The second point I would make is that an "average" bitrate value only
> makes sense in the case of something that varies - a constant bitrate
> has no need of an average, but I guess that's something we can blame
> the specification authors for.

Sadly, yes...

lu



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