[pulseaudio-discuss] Bluetooth aptX codec

[Pali Rohár]

On Wednesday 20 June 2018 17:35:42 Jan Alexander Steffens wrote:
> On Mon, Jun 18, 2018, 09:42 Pali Rohár <pali.rohar at gmail.com> wrote:
> 
> > On Sunday 17 June 2018 23:48:42 Arun Raghavan wrote:
> > > On Sun, 17 Jun 2018, at 4:01 AM, Pali Rohár wrote:
> > > > Hi! As you may know lot of bluetooth headsets support not only SBC, but
> > > > also aptX codec. And new version of ffmpeg (4.0) has native aptX and
> > > > aptX HD encoder and decoder. AptX codec itself is proprietary, but
> > > > ffmpeg has clean-room implementation based on expired patent. What
> > about
> > > > adding support for aptX via ffmpeg into pulseaudio?
> > > >
> > > > --
> > >
> > > I'd actually like to delete the SBC code and replace it with a generic
> > GStreamer bin. That would allow us to be codec agnostic, and support any of
> > the codecs that are supported by GStreamer (which includes those that
> > ffmpeg provides).
> >
> > This does not sound like a good idea. The only two relevant bluetooth
> > codecs for most people are SBC and aptX.
> >
> 
> Don't forget AAC. I've seen this one a lot in devices meant for use with
> iPhones, which apparently don't have aptX. GStreamer has a lot of encoders
> for it so this shouldn't be a problem unless it's some strange AAC variant.
> 
> There's also LDAC but I haven't seen it on a device yet.

I did some investigation and basically this is the list of all known
codecs used in A2DP:

Mandatory:
0x00 - SBC

Optional:
0x01 - MPEG-1,2 (aka MP3)
0x02 - MPEG-2,4 (aka AAC)
0x04 - ATRAC

Vendor specific:
0xFF 0x004F 0x01 - aptX
0xFF 0x000A 0x01 - FastStream
0xFF 0x000A 0x02 - aptX Low Latency
0xFF 0x00D7 0x24 - aptX HD
0xFF 0x012D 0xAA - LDAC

And also I found some references that some sort of raw 16bit PCM samples
via codec id 0x05 are used... But I have never seen such product.

-- 
Pali Rohár
pali.rohar at gmail.com
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