[FFmpeg-devel] GSoC 2008 qualification task

[Kostya]

On Sun, Mar 30, 2008 at 06:49:58PM +0200, Tomasz ?ernicki wrote:
> 
> 
> 
> Dnia 30 marca 2008 15:42 Kostya <kostya.shishkov at gmail.com> napisa?(a):
> 
> > On Sun, Mar 30, 2008 at 01:01:53PM +0200, Tomasz ?ernicki wrote:
> > > Dear All,
> > > Currently I?m trying to figure out how does the transforms in Nellymoser Asao codec work. 
> > > Due to forthcoming deadline of GSoC 2008, I would like to know what are your expectations
> > > connected with "AAC-LC Encoder" task? 
> > 
> > My expectations are that I will do it :)
> > 
> > And more seriously, here is the list of requirements I think everybody will agree with.
> > 
> > General requirements:
> >  * encoder should be able to write data that AAC decoders can understand and play
> >  * sound should be recognizable and preferably not very distorted
> >  * encoder should perform fast (comparing with libfaac and other encoders)
> > 
> > Code requirements:
> >  * encoder should be clean and extensible (maybe somebody will want to add SBR or
> >    other HE-AAC features)
> >  * encoder parameters should be easy to manipulate
> > 
> > > What does exactly mean "flexible framework for a serious psychoacoustic implementation"?
> > 
> > Encoder should have some kind of interface to psychoacoustic models
> > implementations, so it can be used in this way (as I see it):
> > 
> > * some option(s) replated to psy model choosing and finetuning
> > * encoder init function calls ff_psy_init() and tells what psy model it wants,
> >   what kind of data to expect (bands, block size?) etc...
> > * encoding calls something like ff_psy_twiddle() to manipulate frequencies in
> >   desired way, then encodes modified data.
> > 
> > So it is not hardcorded into encoder ("let's throw away all high frequencies")
> > but can be tuned independently and reused in other encoders.
> > 
> 
> So, if I understand, the task is to implement full AAC-LC encoder, am I right? 

Yes

> What about using code from faac encoder which is under LGPL license? 
> Is it possible to use a part of the faac code in a new implementation of AAC encoder?

Theoretically it's possible, but it should be fully
libavcodec-integrated encoder, so most functions should be
rewritten - bitstream writing, transform. So it is easier
to write it from scratch. Nothing can stop you from looking
into faac code though.
 
> Greetings
> Tomasz ?ernicki