Frame rate enumeration ioctl

[Laurent Pinchart <laurent.pinchart (at) skynet.be>]

> > We've been trying to improve the way that the GStreamer V4L2 source
> > handles frame rates when used with webcams. Given that GStreamer uses
> > capability negotiation, we ran into the problem of retrieving a list of
> > supported framerates.
> >
> > Currently, there seems no way (except for trial and error) of enumerating
> > the frame rates that a device supports.
> >
> > We'd like to propose a new ioctl that allows enumerating the supported
> > frame rates for the currently used capture format (e.g.
> > VIDIOC_ENUM_FRAMERATE). If there's interest, we can write up a draft. It
> > would greatly simplify things for applications like GStreamer, Ekiga,
> > etc. that work with webcams.
> >
> > Thanks in advance for any comments ...
> >
> > Cheers,
> > Martin
> >
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> Martin,
> Instead of create a new ioctl() as v4l2 have a lot :) why not used
> VIDIOC_ENUM_FMT to pass parameters the apps need to know from the hardware
> ? If we know that the hardware support for example YUYV for 1024 x 768 is a
> range of framerate min to max is enought ?
> Cheers,

Because VIDIOC_ENUM_FMT doesn't currently support those extra parameters, and 
changing the ioctl would break binary compatibility.

I'm not sure if we should add a new ioctl to handle frame rate enumeration 
only, or create a new "extended" VIDIOC_ENUM_FMT with additional information. 
Mauro, any opinion ?

Laurent Pinchart

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