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List:       linux-video
Subject:    Re: [video4linux] Patchs for bttv-0.5.8
From:       Richard Guenther <zxmpm11 () student ! uni-tuebingen ! de>
Date:       1998-05-17 10:14:41
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On Sat, 16 May 1998, Alan Cox wrote:

> > Another problem is that the semantics of the grabbing (VIDIOCMCAPTURE
> > and VIDIOCSYNC) does not seem to be well defined and easy to use, in
> > particular for 25 fps PAL/SECAM capturing. Why not doing a single ioctl
> > which waits until the current grabbing is finished and begin a new one ?
> > Do you think it could be useful that I submit such a patch ?
> 
> Because normally video applications want to run double buffered - capturing
> in one buffer while processing the other. As soon as they finish processing
> they MSYNC then go on a buffer.

We are using the Matrox Meteor card with the meteor driver. The
meteor driver supplies a ringbuffer for frames and supports
signalling the process if a new frame got grabbed. The ringbuffer
is especially useful, if you can't guarrantee to finish work on
a frame as another arrives, with the ringbuffer approach in this
case you just skip one or two frames and continue with the most
recent one.

I.e. I would suggest a way to set up a reasonable sized ringbuffer,
a way to go into 'continously grabbing'-mode and support
synchronisation by signalling the user process.


What I really need for the V4L API is a (standard) way to grab
the various YUV formats (YUV422 is not enough, as packed
formats are not nice to handle - YUV32 (8(16) bits Y and 8 bits
U and V) is nice for our tasks). It would be useful to support selecting
the color format using a string (?) like "YYUV", as the bt848
chip can switch bytes as we like - even the planar modes seem
to be very useful in high-performance image processing applications.


Richard.

--
Richard Guenther <richard.guenther@student.uni-tuebingen.de>
PGP: 2E829319 - 2F 83 FC 93 E9 E4 19 E2 93 7A 32 42 45 37 23 57
WWW: http://www.anatom.uni-tuebingen.de/~richi/

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