[pulseaudio-discuss] Extra A2DP codecs support in bluetooth module

Pali Rohár pali.rohar at gmail.com
Mon Dec 17 21:47:25 UTC 2018

On Sunday 22 July 2018 13:37:06 Pali Rohár wrote:
> On Sunday 22 July 2018 11:52:11 Georgi Boiko wrote:
> > For codecs focusing on latency over sound quality, if I absolutely had to
> > support them, I would put AptX LL between AptX and AAC. FastStream seems to
> > be even more niche and focused purely on voice over HiFi audio on just a
> Information which I have about FastStream: It is just SBC codec with
> following parameters: frequency rate 44.1 kHz or 48.0 kHz, Blocks 16,
> Sub-bands 8, Joint Stereo, Loudness and Bitpool = 29. So data rate = 212
> kbps, packet size = 72*3+4 = 220 = DM5 and that DSP decoders round 71
> bytes frames to 72 bytes. So I'm not sure how "low latency" it is.
> Normal SBC codec allows you to specify all those parameters. But
> FastStream has one additional feature: it supports backchannel for
> voice, so you do not have to switch between HFP/HSP and A2DP once you
> have incoming voice call. You can always use just A2DP with FastStream.

And information about aptX Low Latency codec: It is just normal aptX
with different A2DP parameters and support for some kind of backchannel.

Therefore existing aptX (non HD) encoder and decoder (like proprietary
Android's, ffmpeg or https://github.com/pali/libopenaptx) are enough for
implementing aptX Low Latency A2DP support.

A2DP structures for aptX Low Latency codec are already described in my
patch, search for a2dp_aptx_ll_t.


Pali Rohár
pali.rohar at gmail.com
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