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List:       linux-video
Subject:    Re: [video4linux] Video capture card advice
From:       Dave Perks <dperks () ibm ! net>
Date:       1998-08-06 12:16:25
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> 
> I've been looking at the Iomega Buz
> and the Matrox Rainbow runner, but I have a few questions that I wanted to
> get some opinions on. The Buz seems pretty cool and I have seen a few
> people on the list comment about it, but I am concerned about some
> information I saw in the documentation for the Zoran chips that it uses.
> According to what I read it appears that to do frame capturing you need a
> contiguous block of memory to store the frame.

I'm working on a Buz driver.  THere are two separate capture modes. One needs
a contiguous buffer but is really intended for viewing the video. It DMAs
the image as YUV or RGB into the video card's frame buffer.  This process
runs continuously with no way of monitoring its progress.  You can however
pause it and take a single snapshot into a contiguous frame buffer elsewhere,
then continue watching TV.  This is nice since in these modes the chip will
do rescaling of the video, handy because the board uses CCIR 601 rectangular
pixels (720 per line) instead of the computer-style square ones (640 per line.)
Actually, odd and even fields can be captured into separate buffers which
might help get around the 128K buffer limit on kernel memory if you don't
capture at maximum resolution.

The main attraction of the board is the JPEG codec.  The DMA mechanism
supporting this easily handles fragmented memory, monitoring of the capture
process, and missed frame detection.  It can deal with up to four buffers in
a ring.

So far my driver (originally based on bttv.c) can watch TV.  I have captured
a couple of JPEG compressed frames into the mmap buffer.  There is still a
lot to be done before the driver is ready for even alpha release.  At least
being able to use it without a reboot afterwards would be nice :-(

I basically stuck to the BTTV interface as of kernel 2.1.109 -- the format
field of the capture currently specifies the desired compressed  size of the
frame but in future a new ioctl should be added, and the sync call returns
the actual length of the data if successful since it will vary.

I'd hoped to release the driver last weekend but things are proceeding slower
than planned and I'm not working on it 7x24 either...  Any suggestions of a
suitable ftp site will be appreciated, I don't have one myself.

-- 
Dave Perks <dperks@ibm.net>
Key fingerprint = EA 37 53 0E FB 0C F0 2D 14 2E 1D 31 D8 E2 A1 27
Sex without love is an empty experience, but, as empty experiences go,
                                 it's one of the best.  -- Woody Allen

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