On 18 Oct 2001, Gerd Knorr wrote:
> > > v4l2 has buffer flags for even/odd field, v4l has not. Is there any way
> >
> > Does it make sense to do v4l2 ? When is it going to make it into the
> > kernel ? (I don't want to require people to patch the kernel in addition
> > to everything else..)
>
> including v4l2 is planned for 2.5.x.
And 2.6.x is still a ways off. What do you think about having "extended
v4l" ? Specifically, I was thinking of adding an extra offset field to
mmap ioctls that would point not to a frame but to a control struct that
would contain fields like timestamp, frame phase (even, odd or something
else), and whatever else is needed. This way read/write operation will be
unchanged, but applications that use mmap can take advantage of extra
features.
best
Vladimir Dergachev
>
> > > to capture both fields interleaved into one buffer? Using pitch =
> > > 2*scanlinelength or something like that? Applications expect the image
> > > interleaved in one buffer ...
> >
> > Not really. (As DMA granularity is 4096 bytes, but pitch is 640*2). I
> > could make it fake this during read but this requires doubling buffers.
> > (4 instead of 2, 1.2meg ram instead of 600k)
>
> Hmm, bad.
>
> > > Any v4l app should work (in theory ...).
> > > There is no test suite (at least I don't know any ...).
> >
> > Well, I just wanted to take the easy way and get this to work with some
> > existing apps instead of implementing ioctl's one by one ;)
>
> As you already have xawtv you can try this one ...
>
> > > Using more (than two) capture buffers basically reduces the risc that
> > > you lose frames on temporary CPU load peaks.
> >
> > Do you know of any apps that actually care about latency issues ?
>
> Videoconferencing is very sensible to latencies, you might have a loom
> at www.openh323.org / gnomemeeting.
>
> Gerd
>
>
>
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