Re: [PATCH] a2dp-codecs: Remove wrong definition of SBC_MAX_BITPOOL

["Pali Rohár" <pali.rohar@gmail.com>]

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On Saturday 26 January 2019 17:25:18 Luiz Augusto von Dentz wrote:
> Hi Pali,
> 
> On Sat, Jan 26, 2019 at 12:47 PM Pali Rohár <pali.rohar@gmail.com> wrote:
> >
> > According to A2DP specification; section SBC; Codec Specific Information
> > Elements; Minimum / Maximum Bitpool Value, range for Bitpool value is from
> > 2 to 250. Decoder shell support 2 as Minimum Bitpool Value and High Quality
> > Bitpool value as the Maximum Bitpool Value at a minimum. A2DP defines
> > maximal High Quality Bitpool value as 53.
> 
> A2DP recommends 53 bitpool for high quality, 64 was used as upper
> bound to limit bandwidth so it had nothing to do with A2DP more like a
> interval detail.

I though that all values in a2dp-codecs.h files matches specifications.
So this value not.

> > Therefore instead of SBC_MAX_BITPOOL macro, defines two macros, one for
> > minimal value of "Maximum Bitpool Value" and maximal value of "Maximum
> > Bitpool Value".
> 
> We could define the recommended bitpools by quality, like the A2DP do,
> and then the MAX to 250, that should make it a bit more clearer.

There are eight recommended bitpool values in A2DP (2x quality; 2x mode;
2x frequency). Do you think that it is useful?

Currently I defined these values in pulseaudio sbc codec in "quality"
structure...

... but seems that a2dp-codecs.h is the place where it should be
defined. So should I put all these recommended values into this file? Or
have it only in pulseaudio?

> > I have no idea what is origin of value 64 as it does not match minimum nor
> > maximum bitpool value. Lot of headsets declares maximum value to 53, so use
> > this value also in android/hal-audio-sbc.c
> 
> We could define 64 as ultra high quality for those that wish a better
> quality than 53, past that there a very limited return in terms of
> quality.

I'm experimenting with value 76 for ultra high quality mode. It has
bitrate 454.8 kbps and minimize unused bytes in A2DP transfer.

But question is, what value do you want to have in file
android/hal-audio-sbc.c? This file is not used on Linux desktop, so I
cannot test this module...

> > ---
> >  android/hal-audio-sbc.c      | 6 +++---
> >  profiles/audio/a2dp-codecs.h | 3 ++-
> >  2 files changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/android/hal-audio-sbc.c b/android/hal-audio-sbc.c
> > index 80e271ed6..541b2d6a7 100644
> > --- a/android/hal-audio-sbc.c
> > +++ b/android/hal-audio-sbc.c
> > @@ -92,7 +92,7 @@ static const a2dp_sbc_t sbc_presets[] = {
> >                 .block_length = SBC_BLOCK_LENGTH_4 | SBC_BLOCK_LENGTH_8 |
> >                                 SBC_BLOCK_LENGTH_12 | SBC_BLOCK_LENGTH_16,
> >                 .min_bitpool = SBC_MIN_BITPOOL,
> > -               .max_bitpool = SBC_MAX_BITPOOL
> > +               .max_bitpool = SBC_MAX_BITPOOL_MIN,
> >         },
> >         {
> >                 .frequency = SBC_SAMPLING_FREQ_44100,
> > @@ -101,7 +101,7 @@ static const a2dp_sbc_t sbc_presets[] = {
> >                 .allocation_method = SBC_ALLOCATION_LOUDNESS,
> >                 .block_length = SBC_BLOCK_LENGTH_16,
> >                 .min_bitpool = SBC_MIN_BITPOOL,
> > -               .max_bitpool = SBC_MAX_BITPOOL
> > +               .max_bitpool = SBC_MAX_BITPOOL_MIN,
> >         },
> >         {
> >                 .frequency = SBC_SAMPLING_FREQ_48000,
> > @@ -110,7 +110,7 @@ static const a2dp_sbc_t sbc_presets[] = {
> >                 .allocation_method = SBC_ALLOCATION_LOUDNESS,
> >                 .block_length = SBC_BLOCK_LENGTH_16,
> >                 .min_bitpool = SBC_MIN_BITPOOL,
> > -               .max_bitpool = SBC_MAX_BITPOOL
> > +               .max_bitpool = SBC_MAX_BITPOOL_MIN,
> >         },
> >  };
> >
> > diff --git a/profiles/audio/a2dp-codecs.h b/profiles/audio/a2dp-codecs.h
> > index 0bdd29110..f31f3a311 100644
> > --- a/profiles/audio/a2dp-codecs.h
> > +++ b/profiles/audio/a2dp-codecs.h
> > @@ -53,8 +53,9 @@
> >  #define SBC_ALLOCATION_SNR             (1 << 1)
> >  #define SBC_ALLOCATION_LOUDNESS                1
> >
> > -#define SBC_MAX_BITPOOL                        64
> >  #define SBC_MIN_BITPOOL                        2
> > +#define SBC_MAX_BITPOOL_MIN            53
> > +#define SBC_MAX_BITPOOL_MAX            250
> >
> >  #define MPEG_CHANNEL_MODE_MONO         (1 << 3)
> >  #define MPEG_CHANNEL_MODE_DUAL_CHANNEL (1 << 2)
> > --
> > 2.11.0
> >
> 
> 

-- 
Pali Rohár
pali.rohar@gmail.com

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