[linux-dvb] reading from demux

[sf <sf@b-i-t.de>]

Hello,

my device is skystar 2.6c (stv0299 + skystar2), kernel version is 
vanilla 2.6.9.

I want to setup demux devices for pid filtering and non-blocking reads 
but I don't succeed.

The setup sequence is:

1. fd = open ("/dev/dvb/adapter0/demux0", O_RDWR);
2. ioctl (fd, DMX_SET_PES_FILTER, &params);
where params is set as following
  params.pid = pid;
  params.input = DMX_IN_FRONTEND;
  params.output = DMX_OUT_TAP;
  params.pes_type = DMX_PES_OTHER;
  params.flags = DMX_IMMEDIATE_START;
3. fcntl (fd, F_SETFL, fcntl (fd, F_GETFL) | O_NONBLOCK);

Then I am polling with select() for data to read and subsequently read a 
multiple of 188 bytes.

The result of the read call is not clear to me:

a) If I request video data, I always get an overflow.
b) If I request at least 188 bytes of audio, I frequently get no 
multiple of 188 bytes.
c) If I request less then 188 bytes of audio, I always get an overflow.

Why does this happen? I would have thought that the demux device always 
 provides data in multiples of 188 bytes because that is how the device 
works. If that were not the case why can't I read less than 188 bytes?

Is the setup sequence not correct?

Regards
	Stephan