video4linux devices

[Richard Hughes]

On Fri, 2006-01-13 at 20:09 +0100, Kay Sievers wrote:
> On Fri, Jan 13, 2006 at 06:35:17PM +0000, Richard Hughes wrote:
> > >From the HAL commit log:
> > 
> > http://cia.navi.cx/stats/project/hal/.message/464b0
> > 
> > I think the new video4linux devices make a lot of sense -- but your
> > comment about "Meaningful properties need to be added by someone who
> > knows about this device class." confused me a little.
> 
> Well, I almost know nothing about video devices. :) I did the same with
> some more properties for the 0.4 HAL, but that never made it into the
> 0.5 version. We need the devices, to let userspace apps receive a list
> of devices and not need to look up device files in /dev. It would be nice,
> if - at best someone writing an app that need video devices from HAL - would
> add or at least tell us, what properties would be useful.

Yes, agreed. Application designers like Kino, Totem, Gnomemeeting and
Cupid should probably use HAL (finding per capabilities) than all
probe /dev/foo with odd v4l1 and v4l2 ioctls.

For instance, if Gnomemeeting could find all devices of capability
"webcam" then it would have a very easy time finding available webcams
-- without picking up my tuner card, for instance.

I think we need to get the application designers involved here.

> > Does this mean we have to add properties from an fdi file, or query the
> > device with a prober using the V4L calls?
> 
> In the 0.4 HAL I used ioctls to query information from the video device.
> There have been may changes to the v4l layer in the meantime and the
> version1 interface is deprecated if I remember correctly, but as said, I
> have almost no clue about video. :)

I think you are correct with v1 ioctls being depreciated, but I'm sure a
prober using v4l2 ioctls could provide a wealth of information about a
device.

Most of the posts on pwc at lists.saillard.org (which I'm subscribed) seem
to be about querying properties for webcams, for example resolutions and
colour depths supported. This would be a big win for a lot of users.

I'm sure the gstreamer guys know quite a bit about devices and v4l2. Can
one of you guys write about this in your blog, and we could get some
interest from interested parties.

Richard.