I am trying to make an alsa output plugin that streams the audio over network (something like esd, just even more simplistic) using the external SDK, however, I am having trouble implementing some things correctly it seems, and the docs weren't descriptive enough.

So far, it works quite well with music playback that doesn't really care about audio blocking, etc. The main problem is audio sync and blocking with more complex applications like MPlayer. As far as I can see in the MPlayer source, to retain audio sync, it uses

snd_pcm_delay() for delay, and snd_pcm_status_get_avail() to figure out how much it can write without audio blocking.

This is fine, but how can snd_pcm_status_get_avail() get the data it needs from the plugins? It doesn't seem to call on any callbacks to do this. It seems so far that snd_pcm_status_get_avail() always returns buffer_size, since I seem to get working audio, but the video starts to stutter. The stuttering goes away when I force a really small maximum buffer size (we're talking 512-ish bytes), but this is really, really bad, and doesn't work too well on my netbook (performance/timing issues I guess). Is it possible to define a snd_pcm_status_get_avail() callback in the SDK in some way?

Anyways. I want to know how you'd do this. The OSS driver for example doesn't even seem to define a delay() callback, which strikes me as odd. How can it know about the delay?

Also, I want to know the reasoning behind the pointer() function. It seems to be called all the time. I don't know what it really does, and what good it does. Is it supposed to represent where in the buffer we are? As in, it's supposed to stay somewhere between 0 and buffer_size? If so, my experience with it doesn't make sense at all. If I return that actual value, the programs simply stop up and loop endlessly over the pointer() function. The temporary "hack" (as in probably very wrong) was to return the total amount of data that's been sent since the start. Can anyone help a frustrated programmer? :P

-- Themaister