[FFmpeg-devel] [PATCH] AAC Encoder, Round 2

Gabriel Bouvigne bouvigne
Mon Aug 25 18:30:36 CEST 2008

Michael Niedermayer a ?crit :

> I agree partially, that is when the parameters are changed its not an
> independant filter but iam not that sure if the parameters should be
> changed ...
> the reason is that significant differences in lowpass or
> stereo attenuation will lead to audible inconsistencies.
> I have not done any listening tests but this is something that would need
> such listening tests IMHO.
> Because IMHO constant stereo attenuation of a signal at a low bitrate that
> could not otherwise be encoded at such bitrate is likely not very annoying
> even if its rather strong, but switching it on and off is almost certainly
> annoying.

For sure, switching between on/off would be very noticeable. That is why 
within the 3gp code, stereo attenuation is not an on/off thing, but 
rather a stereo attenuation factor that is possibly gradually changed 
over several frames.
The key point is that you don't know if any signal will be easy or hard 
to encode at a specific bitrate, you only know if the current signal is 
easy or hard, and the signal changes over time.

Gabriel Bouvigne
personal page: http://gabriel.mp3-tech.org

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