[Ffmpeg-devel] video4linux2 input format?
Thu Jan 26 12:57:52 CET 2006
On Thu, 2006-01-26 at 12:56 +0100, Luca Abeni wrote:
> Thanks; I'll have a look at it today, to check if I got the v4l2 abi
The problem is actually that the api is not 100% specified and some
things can be interpreted in various ways. Only the source knows
Positive thing here is that the drivers for bttv, saa7134 and cx88 are
all written by Gerd Knorr and behave very similarly, although not always
as expected ;-)
> > Please note: the current implementation uses memory mapped i/o, which
> > means memory is allocated by the kernel and passed to the user process.
> Yes, this is what I am doing too: first, I want to have mmap working,
> then I'll implement read-based grabbing (for very old card or broken
> drivers?), and then I'll try the pointer-based I/O. The problem with it
> is that the demo program included in the v4l2 specifications just
> crashed my computer (debian unstable, 2.6.8 kernel, and a Bt878-based
> card)... So, I assume the specifications are not very reliable regarding
> pointer-based I/O ;-)
Or maybe the demo program is obsolete, who knows. The way you setup
stuff is very critical indeed, because of the whole nature, this close
to the hardware, although a perfect implementation off course never
crashes ;-) I had it working using 2.6.6 or something like that. The
read-based grabbing is actually not workable, it delivers about 1 frame
per second. Also afaik there are no drivers that only support the read()
interface. Please reconsider using it.
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