Paul Davis <[EMAIL PROTECTED]> wrote > >Hello, > >is it possible to get a callback after a specified number > >of samples (e.g. 4000) are played? > >I'd like to refill the buffer then and need the exact > >number to synchronize audio and video. > > you can get this to a limited extent by setting the software parameter > "avail_min" with snd_pcm_sw_params_set_avail_min(). it controls the > number of frames of data/space that has to be available for a task > sleeping on a read/write of the PCM stream to be woken up. > > however, it won't do what you want, because the resolution is limited > to the interrupt frequency of the audio card, and for just about every > interface out there, this is almost always a power of 2 value.
Is this an Alsa design or a hardware limitation? > thus, > you could set avail_min to 4000, but you be will woken only when the > actual value is 4096, not 4000. why? because the ALSA driver has no > way of knowing when the value is 4000 - it can only know when the > interrupt comes in. > > the only way around this is to use an alternate, higher-frequency > interrupt source, such as the RTC (real time clock), but this > is invariably power-of-2 also, and worse, doesn't run in sync > with audio or video. if you could find a suitable source, you just > check the current frames/space available every interrupt, and move on > from there. i don't know of any suitable interrupt sources. > > to put it another way, your approach is wrong :) syncing audio and > video needs to be done differently. audio has a much higher frame > rate, so use that as the basic time source, and simply redraw the > screen at suitable intervals (preferably the vertical refresh > interval), using the current audio "time" as a guide to what to draw. You think of polling snd_pcm_avail_update and drawing the picture when the calculated number of samples have been played? ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
