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

["Edward Wildgoose" <Ed@Wildgooses.com>]

> > I have a full card with decoder, so I get a /dev/video1 v4l device (I'm
> > under 2.4.20 with the standard v4l checkout from CVS).
>
> Why do you get /dev/video1?
>
> Do you have multiple dvb cards or other v4l cards (ie. bt8x8 cards)?

I have a bt8x8 card which grabs /dev/video0

>
> >  However, Mythtv
> > is calling this line of code and failing with "invalid parameter":
>
> >   if (ioctl(fd, VIDIOCMCAPTURE, &mm)<0)
> >       perror("VIDIOCMCAPTURE0");
>
> So, mythtv is really using v4l. I'm sorry, but there could be multiple
> reasons while this fails.  8-(

Fair enough.

>
> > 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.
>
> Because of the fact that I'm the "v4l2 guy", I can only say that "nvrec"
> can record from the "dvb-kernel" v4l2 driver, but this won't help you
> for mythtv, I admit.
>

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.

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?

> As I already said above, v4l2 has nothing to do with MPEG at all.

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...!)

Thanks for clearing that up

>
> > So can the latest v4l2 driver for the DVB-T card do this as well?  ie if
> > I upgrade my kernel to 2.4.20 with the v4l2 patches and grab the 2.5
> > kernel branch of the driver will I get a /dev/video1 device which can
> > spit out MPEG 2?
>
> No. If mythtv only supports v4l1, all capturing stuff will go through
> the compatiblity layer, which is know to slow things down.
>

I think it has some support for v4l2.  However, ideally I would like to work
on support for capturing the MPEG stream directly into myth.  The author of
the program is adding support for mpeg via the ivtv driver and so I think
that most of the groundwork has been done and I just need a simple external
tuner module.

This should give basically the same functions as vdr, but with software
output.  Myth also has support for epg via xmltv (which I don't think is in
vdr?).  And also it supports lots of eye candy because it is designed for
output via monitor only.  However, it misses lots of the nice stuff from vdr
like support for lcd displays, multicasting the output, and mpeg decoder
support.  If I can get DVB support into it though, then it will at least be
a credible alternative I think.


> 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.  Sorry for the stupid
questions!

If you are interested you may also want to check out the MpegRecord.cpp in
libs/mythtv from the CVS version which appears to be the module which
accesses the ivtv driver.  It looks as though it would be straightforward to
modify this to add support for DVB and this is what I intend to try first.



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