[Ffmpeg-devel] video4linux2 input format?

Erik Slagter erik
Thu Jan 26 12:27:35 CET 2006

On Wed, 2006-01-25 at 14:48 +0100, Luca Abeni wrote:
> someone managed to scare me telling me that video4linux support will be
> removed from future linux kernels... So, I think libavformat rally needs
> video4linux2 support.

Right on, finally! It has been marked "obsolete" for ages (I mean,
really, we're talking > 5 years)!

> Is anyone already working on it? If not, I'll start implementing
> video4linux2 support today (I am asking just to avoid duplicate work).
> As usual, pointers to useful information are apreciated :)
> (I am currently reading http://v4l2spec.bytesex.org/spec )

Good work! The specs on bytesex are quite good, but are not 100% in sync
with reality :-( (although it doesn't differ that much).

Please have a look at the the file import/v4l/import_v4l2.c from
transcode (version > 0.6.14), which [ahem] I wrote and has some
workarounds for these ehrm... "extra features". The source is not very
much dependent on any other parts of the transcode source, so it
shouldn't be too hard to follow.

Please note: the current implementation uses memory mapped i/o, which
means memory is allocated by the kernel and passed to the user process.
This is not that bad, but nowadays there is also another method
available, called "user pointers", which allows the user process to
allocate memory and have that filled by the device, which allows for
zero-copy operation. I would certainly to try use that if it's possible.
I tried it with the saa7134 and for me it worked fine.

As I am no longer using v4l2 (switched to DVB-S, saa7134 card fried
itself), I cannot help you with the actual coding and testing etc :-(

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