Hi, I'm in the process of porting PJSIP to an ARM-based device, and I ran into a problem with sound playback, which I was not able to figure out so far. The device's sound API requires me to completely fill a fixed-sized playback buffer with samples, which I receive by calling the PJMEDIA's play_cb callback. The size of the buffer is larger than size of the frame which play_cb returns, so normally 6 or 7 calls to play_cb are required to fill the device's buffer. The problem is that if I do so many callback calls in a loop, I inevitably get a few log messages like that: 08:32:42.082 Master/sound Underflow, buf_cnt=0, will generate 1 frame 08:32:42.083 Master/sound Underflow, buf_cnt=0, will generate 1 frame 08:32:42.086 Master/sound Underflow, buf_cnt=0, will generate 1 frame 08:32:42.088 Master/sound Underflow, buf_cnt=0, will generate 1 frame 08:32:42.088 Master/sound Underflow, buf_cnt=0, will generate 1 frame 08:32:42.091 Master/sound Underflow, buf_cnt=0, will generate 1 frame 08:32:42.112 Master/sound Underflow, buf_cnt=0, will generate 1 frame I assume that I'm asking for more data than PJMEDIA layer currently has, and it generates some frames in order to keep up with data requests. Not sure what algorithm is used to generate them, but it results in a pretty choppy sound, with a few interruptions per second. That's my analysis of the problem anyway, I could be completely wrong :-). What I would like to do it is somehow instruct the PJMEDIA layer to just wait for more sound samples to become available, instead of returning the generated frames, when it is out of it. However, I could not really find a mechanism to do it by looking at the code: the play_cb callback is non-blocking (as far as I can tell) and always returns PJ_SUCCESS, independently of whether the data it returns was real or generated. I've looked at some other sound drivers (like pasound.c), and it appears that they use pretty much the same algorithm, i.e. calling the play_cb callback multiple times to fill up the buffer. So, presumably, it should work somehow, so it's possible that I'm doing something wrong. Any ideas would be appreciated. Thanks. -- Jurij Smakov jurij at wooyd.org Key: http://www.wooyd.org/pgpkey/ KeyID: C99E03CC
