[linux-dvb] Re: V4L interface to the MPEG stream?

[Michael Hunold <hunold@convergence.de>]

Hello Edward,

> I have a bt8x8 card which grabs /dev/video0
Ok.

> > I'll check out mythtv and tell you my results in getting it to
> > run, both
> > with the DVB driver and the dvb-kernel driver. Please be patient.
>
> That would be really kind.  Thanks for your help.
After installing tons of stuff (qt, mysql, setting it all up) I got
Mythtv running with the dvb-kernel driver.

> > > However, Mythtv
> > > is calling this line of code and failing with "invalid parameter":
> > >  if (ioctl(fd, VIDIOCMCAPTURE, &mm)<0)
> > >      perror("VIDIOCMCAPTURE0");
As I expected, running it through the v4l1 compatibility layer slows the
capture down massively. I know how to fix that but I don't have the time
for it currently, because it requires bigger changes. (I have to peek at
bttv/saa7134 and see how Gerd Knorr does it...)

> > > and this is actually code out of nuvrec, so although I haven't tried, I
> > > assume that nuvrec would also fail to record from this v4l interface.
Perhaps.

> Great, I believe that the mythtv recording code is directly from nvrec (I
> could be wrong), so I guess that this may be a v4l1 compatibility problem.
Unless people port their applications to v4l2, there will always be
compatibility problems with the saa7146. I think Gerd Knorr has put much
energy in making his new bttv/saa7134 drivers work with v4l1, but I
don't have the time to mess with that. IMHO all applications which need
decent capture timing and performance should use v4l2. Perhaps this will
improve with 2.6 kernels.

> I believe that I can run the v4l2 DVB code on 2.4.20 if I apply the v4l2
> patches first?  Perhaps this is worth a try?
Perhaps. You can download "dvb-kernel" from CVS and compile and run it
locally without installing. Just make sure you load the right frontend
driver manually if necessary.

> Great, I think that is the answer I need.  There is a driver for the PVR250
> cards (http://ivtv.sf.net) which "appears" to spit the output as mpeg 2 via
> a v4l interface.  I wasn't sure why this was and whether there was something
> significant in v4l2 which made them do it this way (a simple socket would
> appear to have been enough...!)
As Gerd Knorr already said, they use the v4l interface to provide the
encoded mpeg2 data stream from the on-board video encoder -- I did not
know that.

I'm sorry, but Mythtv is really a big piece of software and I don't have
any ideas what could cause your problems. Perhaps it's best when you do
a step by step analysis (ie. only use the dvb card, not the bttv one)
and see what happens. The "old" DVB driver is plain v4l, so it should
basically work. But this driver was written before I joined the team, so
I won't support it.

CU
Michael.




--
Info:
To unsubscribe send a mail to listar@linuxtv.org with "unsubscribe linux-dvb" as subject.