Re: [Bluez-devel] AVDTP socket?

Brad Midgley
2004-11-07T18:55:59Z

Marcel

>>What I wanted to do was start by using the reference SBC codec or just
>>one of the reference streams (cleverly hidden in the *zipfile*
>>A2DP_TS.pdf at bluetooth.org) and then experiment with sending it to the
>>headset.
>
> I looked a little bit into ALSA and actually what we really need is the
> support in the ALSA library for understanding SBC. So the kernel don't
> has to worry about it.

good, so it's an alsa project. :)

in the perfect world, you should be able to hand an mp3 over to a
userspace library that only transcodes into SBC if the headset does not
advertise its own mp3 codec. same with aac. avoiding the transcode would
be good for reducing latency and preserving batteries on a portable
player. it may be academic if none of the headsets implement optional
codecs.

>>I'm looking at the diagram on p. 17 of the A2DP spec... it looks like
>>the AVDTP layer takes the encoded stream, breaks it up and puts the
>>media packet headers on it. Is that right?
>
>
> In general yes, but the AVDTP is crap. It needs at least two L2CAP
> channels on PSM 25.

it may be ugly, but it's all we've got, eh?

>>I am a little confused about this though... does this show the A2DP sink
>>as using the rfcomm protocol?
>>
>>$ sdptool search --bdaddr 00:08:F4:30:05:BB 0x1101
>>Class 0x1101
>>Searching for 0x1101 on 00:08:F4:30:05:BB ...
>>Service Name: Audio Sink
>>Service RecHandle: 0x10005
>>Service Class ID List:
>> "Serial Port" (0x1101)
>>Protocol Descriptor List:
>> "L2CAP" (0x0100)
>> "RFCOMM" (0x0003)
>> Channel: 1
>
>
> I saw that too and actually I don't know what is it good for. Maybe you
> wanna try to connect it to a TTY and then copy the SBC files into it.

I copied a few of the sbc streams. They resulted in a whole lot of
static on the headset. I think we need to tell the headset we're using
avdtp and get that media packet header in there.

I don't know where to start with the avdtp protocol handling. Can you
give me a pointer?

Brad

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