[linux-dvb] Re: Adding V4L interface to budget cards

[Ralph Metzler <rjkm@metzlerbros.de>]

Holger Waechtler writes:
 > Ralph Metzler wrote:
 > > Rene Bartsch writes:
 > >  > after reading documentation of new FFMPEG 0.4.6 I got the idea to add a
 > >  > libavfomat-based V4L-device to the DVB-driver, which decodes TS to standard
 > >  > YUV (or whatever is used on the V4L-interface).
 > >  > 
 > >  > This would allow programs like XawTV to watch TV without having a own
 > >  > MPEG-TS decoder. Standard TV-software could handle the DVBs like a analogue
 > >  > TV-card (except tuning-parameters, of course).
 > >  > 
 > >  > Comments?
 > > 
 > > Software decoding should not be put into the kernel.
 > > Other drivers (USB webcam) had simple color conversions thrown out
 > > when they were integrated into the kernel. They also had the
 > > conversion in the driver to make it easier for applications which
 > > could only handle certain color formats. I think the outcome of the
 > > discussion on the V4L list was that a standard user library should
 > > handle this. 
 > > 
 > > You could also use vloopback to do the decoding in userspace but still
 > > have a V4L device with the decoded result.
 > 
 > The problem is not the v4l interface, this can get faked easily by a 
 > userspace library API.
 > 
 > Kernel space codec libraries get interesting when you start to replace 
 > the so called firmware libraries or 'BIOS'es by an own implementation. 
 > Those are basically a 'ffmpeg with some hardware acceleration hooks' 
 > running in kernel space.

[...]

 > Maybe at the end we will stay stuck with the proprietary firmware 
 > libraries which do essentially the same, but they are 'politically more 
 > accepted', just because there is much more black voodoo around them and 
 > you can't get rid of them so fast...


But the question was about plugging the current ffmpeg libraries into
the DVB driver to provide a V4L interface and not about a general DSP 
hardware interface infra-structure. The former is not really a good idea. The
latter is useful only if hardware (including documentation) for such purposes
is actually available. Currently access to such hardware is mostly 
proprietary and companies do not even use available standard
interfaces with their binary drivers (see e.g. DRI and nVidia or the
once promised ATI hardware iDCT libraries).


Ralph


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