Re: [Bluez-devel] a2dp timing

Re: [Bluez-devel] a2dp timing

[Mayank Batra]

Hi Brad,

> I suppose we could implement a2dp sink as well, but
> I don't think 
> connections can be initiated by a sink--it has to
> listen for the source 
> to make the connection.

I am working on the A2DP sink. Ofcourse the connection
has to be initiated by the source.
Right now the sound quality is not good.
Can you help me out in improving the sound quality ?
 
Mayank

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Re: [Bluez-devel] a2dp timing

[Brad Midgley]

Mayank,

do you have a helper app like a2play that negotiates the avdtp protocol?

i would like to, yes. if you're willing to make it GPL, can you send the 
source to me directly and i'll put it in cvs?

are you using a2play or one of the dongles to test your sink? i don't 
have access to a dongle any more.

brad

Mayank Batra wrote:
> Hi Brad,
> 
> 
>>I suppose we could implement a2dp sink as well, but
>>I don't think 
>>connections can be initiated by a sink--it has to
>>listen for the source 
>>to make the connection.
> 
> 
> I am working on the A2DP sink. Ofcourse the connection
> has to be initiated by the source.
> Right now the sound quality is not good.
> Can you help me out in improving the sound quality ?
>  
> Mayank
> 
> ________________________________________________________________________
> Yahoo! India Matrimony: Find your life partner online
> Go to: http://yahoo.shaadi.com/india-matrimony
> 
> 
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Re: [Bluez-devel] a2dp timing

[Mayank Batra]

Brad,
 
> do you have a helper app like a2play that negotiates
> the avdtp protocol?

Yes I am using a2play application as well as a Windows
 application BlueSoleil by IVT Corporation to
negotiate the avdtp protocol. The connection is
working alright. The problem is just the sound
quality.

 
> i would like to, yes. if you're willing to make it
> GPL, can you send the 
> source to me directly and i'll put it in cvs?

I am not sure right now about the GPL part.
Will tell you in a few days.


> are you using a2play or one of the dongles to test
> your sink? i don't 
> have access to a dongle any more.

I am using dongles. :-(



Mayank

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Re: [Bluez-devel] a2dp timing

[Henryk Plötz]

[-- Attachment #1: Type: text/plain, Size: 515 bytes --]

Moin,

Am Fri, 15 Apr 2005 10:41:46 +0100 (BST) schrieb Mayank Batra:

> negotiate the avdtp protocol. The connection is
> working alright. The problem is just the sound
> quality.

I'd be very interested in helping with this code, too. And I also still
have the audio dongle from my headset, so I could test with that.

-- 
Henryk Plötz
Grüße aus Berlin
~~~~~~~ Un-CDs, nein danke! http://www.heise.de/ct/cd-register/ ~~~~~~~
~ Help Microsoft fight software piracy: Give Linux to a friend today! ~

[-- Attachment #2: Type: application/pgp-signature, Size: 189 bytes --]

[Bluez-devel] a2dp timing

[Brad Midgley]

Hi

We've had problems with a2dp timing that I've been ignoring.

For one, a2play crams frames into the headset just as fast as it can. 
Sometimes this is too fast. So we need to clock it so things are 
staggered properly. Does the SBC encoder give us a clue about timing 
between frames?

Second, if the headset wanders out of range, the player stops and starts 
up where it left off when the headset is back. If we're pacing things 
properly, we need to drop frames instead when this happens. I'm thinking 
if it results in a legal SBC stream that I'll drop entire SBC frames in 
the main loop with something like:

	frame_len = read_header(fd, &sbc_info);
	bytes_read = read(fd, killbuffer, frame_len);

Are there other timing issues I need to think about? Does it get so 
messy that I need to watch jitter? I can only vaguely remember this 
stuff from my networking classes...

Brad


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Re: [Bluez-devel] a2dp timing

[Marcel Holtmann]

Hi Brad,

> We've had problems with a2dp timing that I've been ignoring.
> 
> For one, a2play crams frames into the headset just as fast as it can. 
> Sometimes this is too fast. So we need to clock it so things are 
> staggered properly. Does the SBC encoder give us a clue about timing 
> between frames?

it would be really great to get a FTS or CATC trace from the HP
headphone and the iPAQ for example.

In the case of an ALSA plugin, we may simple use the timing of the ALSA
system itself. However it would be great if the SBC encoder would also
calculate the time of the PCM fragment.

> Second, if the headset wanders out of range, the player stops and starts 
> up where it left off when the headset is back. If we're pacing things 
> properly, we need to drop frames instead when this happens. I'm thinking 
> if it results in a legal SBC stream that I'll drop entire SBC frames in 
> the main loop with something like:
> 
> 	frame_len = read_header(fd, &sbc_info);
> 	bytes_read = read(fd, killbuffer, frame_len);

And then you need to sleep some time before reading/dropping the next
SBC frame.

> Are there other timing issues I need to think about? Does it get so 
> messy that I need to watch jitter? I can only vaguely remember this 
> stuff from my networking classes...

I don't think that this will be needed, but we will see.

Regards

Marcel




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Re: [Bluez-devel] a2dp timing

[Guylhem Aznar]

On Friday, 25 March 2005 at 14:14:36 (+0100), Marcel Holtmann wrote:
> it would be really great to get a FTS or CATC trace from the HP
> headphone and the iPAQ for example.

Please tell me how to do it. I will be happy to help.
However I don't have the bluesoleil stack....

--=20
Bien =E0 vous - Best regards,
Guylhem P. Aznar

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Re: [Bluez-devel] a2dp timing

[Marcel Holtmann]

Hi Guylhem,

> > it would be really great to get a FTS or CATC trace from the HP
> > headphone and the iPAQ for example.
> 
> Please tell me how to do it. I will be happy to help.
> However I don't have the bluesoleil stack....

do you have the Frontline FTS4BT or the CATC Merlin II sniffer?

Regards

Marcel




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Re: [Bluez-devel] a2dp timing

[Guylhem Aznar]

On Friday, 25 March 2005 at 15:26:12 (+0100), Marcel Holtmann wrote:
> > However I don't have the bluesoleil stack....
>=20
> do you have the Frontline FTS4BT or the CATC Merlin II sniffer?

Looks like it's dedicated hardware - nope. I though some software
sniffing was possible (ala tcpdump with hcidump)

--=20
Bien =E0 vous - Best regards,
Guylhem P. Aznar

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Re: [Bluez-devel] a2dp timing

[Marcel Holtmann]

Hi Guylhem,

> > > However I don't have the bluesoleil stack....
> > 
> > do you have the Frontline FTS4BT or the CATC Merlin II sniffer?
> 
> Looks like it's dedicated hardware - nope. I though some software
> sniffing was possible (ala tcpdump with hcidump)

not for air sniffing and that is what you actually need in this case.

Regards

Marcel




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Re: [Bluez-devel] a2dp timing

[Brad Midgley]

Marcel

> In the case of an ALSA plugin, we may simple use the timing of the ALSA
> system itself. However it would be great if the SBC encoder would also
> calculate the time of the PCM fragment.

ok, I will look at the plugin again. I was discouraged before by the 
complexity and by the fact that a lot of alsa clients won't let you 
choose a userspace plugin device (and even with those that do, you have 
to remember and type in an alsa device name to reach a userspace plugin)

>>	frame_len = read_header(fd, &sbc_info);
>>	bytes_read = read(fd, killbuffer, frame_len);
> 
> And then you need to sleep some time before reading/dropping the next
> SBC frame.

of course from the plugin, these won't be read() calls, they will be 
calls into the sbc lib.

brad


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Re: [Bluez-devel] a2dp timing

[Marcel Holtmann]

Hi Brad,

> > In the case of an ALSA plugin, we may simple use the timing of the ALSA
> > system itself. However it would be great if the SBC encoder would also
> > calculate the time of the PCM fragment.
> 
> ok, I will look at the plugin again. I was discouraged before by the 
> complexity and by the fact that a lot of alsa clients won't let you 
> choose a userspace plugin device (and even with those that do, you have 
> to remember and type in an alsa device name to reach a userspace plugin)

the flag for that is there, but the ALSA core does not use it. Seems
like I need to remind Takashi to add it.

> >>	frame_len = read_header(fd, &sbc_info);
> >>	bytes_read = read(fd, killbuffer, frame_len);
> > 
> > And then you need to sleep some time before reading/dropping the next
> > SBC frame.
> 
> of course from the plugin, these won't be read() calls, they will be 
> calls into the sbc lib.

In case of the plugin you can simply drop the PCM fragment.

Regards

Marcel




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Re: [Bluez-devel] a2dp timing

[Brad Midgley]

Marcel

FYI, I found alsa-lib post-1.0.8 has fixed up the plugin api so plugins 
really can be built standalone. The plugins were moved to a different 
cvs project "alsa-plugins" and the api changed in the process.

I changed our reference plugin to be based on the new oss plugin. I will 
work on the a2dp source side of things here. It looks much more 
straightforward now.

I suppose we could implement a2dp sink as well, but I don't think 
connections can be initiated by a sink--it has to listen for the source 
to make the connection.

I'm keeping the cvs code up to date in case anyone wants to look (in 
btsco/bt)

On a more pragmatic note, I sold my bluetake to a friend so it won't be 
as easy to try things on it. I bought one of the iTech sets so hopefully 
development can go well with the new headset.

Brad


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Re: [Bluez-devel] a2dp timing

[Marcel Holtmann]

Hi Brad,

> FYI, I found alsa-lib post-1.0.8 has fixed up the plugin api so plugins 
> really can be built standalone. The plugins were moved to a different 
> cvs project "alsa-plugins" and the api changed in the process.

I know and actually the utils CVS already contains a plugin for SBC over
RFCOMM. Was a simple proof-of-concept thing.

> On a more pragmatic note, I sold my bluetake to a friend so it won't be 
> as easy to try things on it. I bought one of the iTech sets so hopefully 
> development can go well with the new headset.

I think we really need the Logitech/HP headphone for further development
and so if anyone wants to support this, do a PayPal donation and then I
will buy one for Brad and me.

Regards

Marcel




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