[vorbis] vbr / cbr / abr API calls

[Akos Maroy]

Michael,

> Right. Remember to call vorbis_info_init(&vorbisInfo) before all of that.

OK. Now that we're on the matter, could you explain the possible 
parameters of vorbis_encode_ctl() ? In vorbisenc.h I see the following:

<p>extern int vorbis_encode_ctl(vorbis_info *vi,int number,void *arg);

#define OV_ECTL_RATEMANAGE_GET       0x10

#define OV_ECTL_RATEMANAGE_SET       0x11
#define OV_ECTL_RATEMANAGE_AVG       0x12
#define OV_ECTL_RATEMANAGE_HARD      0x13

#define OV_ECTL_LOWPASS_GET          0x20
#define OV_ECTL_LOWPASS_SET          0x21

#define OV_ECTL_IBLOCK_GET           0x30
#define OV_ECTL_IBLOCK_SET           0x31

<p>I understand these constants are the possible parameters for number in 
the call to vorbis_encode_ctl().

<p>OV_ECTL_RATEMANAGE_GET

arg is expected to be a pointer to a struct ovectl_ratemanage_arg.
fills in the supplied struct ovectl_ratemanage_arg, representing the 
current settings for rate management

OV_ECTL_RATEMANAGE_SET

arg is expected to be a pointer to a struct ovectl_ratemanage_arg.
sets rate management specified by the settings in the supplied arg. if 
arg == 0, sets non-managed mode

OV_ECTL_RATEMANAGE_AVG

arg is expected to be a pointer to a struct ovectl_ratemanage_arg.
sets some things related to the bitrate_av_* values in arg?

OV_ECTL_RATEMANAGE_HARD

arg is expected to be a pointer to a struct ovectl_ratemanage_arg.
sets some thins related to bitrate_hard_* values in arg?

OV_ECTL_LOWPASS_GET

arg is expected to be a pointer to a double.
fills in the supplied double with the current value for lowpass 
filtering (supposedly in Hz? or kHz?)

OV_ECTL_LOWPASS_SET

arg is expected to be a pointer to a double.
sets current value for lowpass filtering (supposedly in Hz? or kHz?) 
supplied by arg

OV_ECTL_IBLOCK_GET

arg is expected to be a pointer to a double.
but what does this return?

OV_ECTL_IBLOCK_SET

arg is expected to be a pointer to a double.
but what does this set?

<p><p>The behaviour of OV_ECTL_RATEMANAGE_AVG and OV_ECTL_RATEMANAGE_HARD 
suggests that members birate_av_* are related to some ABR-style 
encoding, while bitrate_hard_* related to a CBR-style (or hard-set 
limits) encoding. How does this work exaclty?

<p>Akos

<p><p>--- >8 ----
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