[alsa-devel] When to start the capture device?

Sheng (Sean) Liu shengl at uci.edu
Fri Sep 21 00:10:12 CEST 2007

Hi Mr. Iwai,

Thanks for your replies. I have another question for you.

After snd_pcm_start() is called, how long the first frame will be generated
by the sound card? Does this duration vary in different nodes (support
hardware+soundcard+OS are identical for all nodes)? If the duration is not a
constant, do you have any idea what will be the largest jitter?

This jitter matters so much for my location detection application.  After
the application starts, an user claps his/her hand. Then, the position of
the user is calculated from the application. 

I have four VIA EPIA-M+Linux2.6 machines. A global time is setup among these
four nodes. After the stream is started, the application detects a hand-clap
sound and counts the number of frames from the stream start to the clap
moment in each node. If I cannot have an accurate timestamp for the stream
start, the application cannot caculate the clap sound timestamp accurately.



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