[FFmpeg-devel] [RFC] AAC Encoder

[Michael Niedermayer]

On Fri, Aug 15, 2008 at 10:11:03AM +0300, Kostya wrote:
> On Thu, Aug 14, 2008 at 11:42:44PM +0200, Michael Niedermayer wrote:
> > > 
> > > enum AACPsyModelMode{
> > >     PSY_MODE_CBR,              ///< follow bitrate as closely as possible
> > >     PSY_MODE_ABR,              ///< try to achieve bitrate but actual bitrate may differ significantly
> > >     PSY_MODE_QUALITY,          ///< try to achieve set quality instead of bitrate
> > > };
> > > 
> > > #define PSY_MODEL_MODE_MASK  0x0000000F ///< bit fields for storing mode (CBR, ABR, VBR)
> > 
> > please use bitrate tolterance/bitrate/max/min bitrate/buffer size/...
> > from AVCodecContext for selecting the mode
> 
> I will, but I will keep those for internal state. 
>  

> > > #define PSY_MODEL_NO_PULSE   0x00000010 ///< disable pulse searching
> > > #define PSY_MODEL_NO_SWITCH  0x00000020 ///< disable window switching
> > > #define PSY_MODEL_NO_ST_ATT  0x00000040 ///< disable stereo attenuation
> > > #define PSY_MODEL_NO_LOWPASS 0x00000080 ///< disable low-pass filtering
> > 
> > How does the user pass these to the codec?
> > I suspect in AVCodecContext, if so above would be redundant and unneeded
> > as AVCodecContext is availabe to the psy model
> 
> huh? I haven't seen flags for such thing in avcodec.h

it was a hyphotetical question
* If noone adds such flags to AVCodecContext the user can not pass them to the
  psy model thus above would be useless
* If one does add such flags to AVCodecContext the above would be redundant


[...]
> > > 
> > > #define PSY_MODEL_NO_PREPROC (PSY_MODEL_NO_ST_ATT | PSY_MODEL_NO_LOWPASS)
> > > 
> > > #define PSY_MODEL_MODE(a)  ((a) & PSY_MODEL_MODE_MASK)
> > > 
> > > /**
> > >  * context used by psychoacoustic model
> > >  */
> > > typedef struct AACPsyContext {
> > >     AVCodecContext *avctx;            ///< encoder context
> > > 
> > >     int flags;                        ///< model flags
> > 
> > >     const uint8_t *bands1024;         ///< scalefactor band sizes for long (1024 samples) frame
> > >     int num_bands1024;                ///< number of scalefactor bands for long frame
> > >     const uint8_t *bands128;          ///< scalefactor band sizes for short (128 samples) frame
> > >     int num_bands128;                 ///< number of scalefactor bands for short frame
> > 
> > This is a little AAC specific but then its called AACPsyContext
> > so iam not sure. Is the code supposed to be a generic psychoacoustic model
> > or AAC specific?
> 
> AAC-specific. I thinks it's possible to make it more generic, but it will require
> some radical changes, especially for window switching code and scalefactors.

ok


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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