Synchronizing with the PCM subchannel

QSA provides some basic synchronization capabilities.

An application can find out where in the stream the hardware capture position is. The resolution of this position is entirely a function of the hardware driver; consult the specific device driver documentation for details if this is important to your application.

The API calls to get this information are:

Both of these functions fill in a snd_pcm_channel_status_t structure. You'll need to check the following members of this structure:

The hardware capture position, in bytes relative to the start of the stream since you last prepared the channel. The act of preparing a channel resets this count.
The capture position as bytes in the hardware buffer.
Note: The count member isn't used if the mmap plugin is used. To disable the mmap plugin, call snd_pcm_plugin_set_disable().