[pulseaudio-discuss] Bluetooth Latency Question

[Baek Chang]

I was thinking about writing data to the output and recording it on the
input and calculating the time it takes.  This would be done on bluetooth
and a non- bluetooth device (regular speakers).  With those two values, get
the ratio of bluetooth to non-bluetooth and just multiplying that by the
latency from pulseaudio.  This value would be used as the delay to sync
audio/video. Wondering if this would help in lip sync and where this value
should go?

"pcm_pulse.c" in alsa-plugins has the function pulse_delay() which returns
the delay.  Can this be modified to reflect this newly acquired delay?  If
not, then where?

Thanks
Baek Chang

On Thu, Jan 22, 2009 at 1:00 PM, Lennart Poettering
<lennart at poettering.net>wrote:

> On Wed, 21.01.09 13:44, Baek Chang (baeksan at ccrma.stanford.edu) wrote:
>
> > How is the latency obtained when using bluetooth in pulseaudio.  By
> latency
> > I mean something similar to snd_pcm_delay().  Since bluetooth doesn't use
> > alsa, how is the time delay calculated from writing data to actually
> hearing
> > it out of the dac?
>
> AFAIK Bluetooth doesn't really offer a sensible way to query the
> current delay, not even a2dp. In fact a2dp doesn't even offer flow
> control.
>
> The clocking part in the PA BT module is currently lacking. I just
> bought myself a bit of BT hardware so that I can hack on this and try
> to work around the limitations of BT a bit.
>
> Lip-sync audio/video with a BT headset is probably not going to
> happen, though. And that is not a limitation of PA but of BT.
>
> Lennart
>
> --
> Lennart Poettering                        Red Hat, Inc.
> lennart [at] poettering [dot] net         ICQ# 11060553
> http://0pointer.net/lennart/           GnuPG 0x1A015CC4
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-- 
Baek Chang
baeksan at ccrma.stanford.edu
407-267-6701
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