[Alsa-devel] Audio and Video sync. Getting Timestamps

[Juan Carlos Granda]

Hi,   I'm developing a Multi-thread app for capturing audio+video and i have a few questions. The app is based on 3 threads:    - 1 thread for capturing audio using ALSA lib.  - 1 thread for capturing video using V4L2.  - 1 thread for saving audio+video into an AVI file.   Both of capturing threads store captured data into a queue and the last thread picks the data and sync A/V.   I start audio capturing and then the video. So, i need to known the point of the stream of audio the video begins. I'm readings frames by period size times. My prob is how to get valid ALSA timestamps to eliminate the previous frames of the period the video starts. I've tried snd_pcm_status_get_trigger_tstamp but it returns the same timestamp for a long period of time (13 secs) (is it related to the period or buffer time?). I've tried snd_pcm_status_get_tstamp too but i obtain a delay of several microseconds from the period time (50 - 100 more or less) (is it because the clock resolution?).   Thanks   pd. Sorry for my little knowledge of english.