[linux-dvb] Start thinking about potential Google Summer of Code Projects we could run

Hans Verkuil hverkuil at xs4all.nl
Wed Dec 19 18:31:43 CET 2007


On Wednesday 19 December 2007 18:23:55 Richard Atterer wrote:
> On Wed, Dec 19, 2007 at 05:36:09PM +0100, Hans Verkuil wrote:
> > I think that this might be an ideal opportunity to develop a v4l2
> > library that can be used by applications to access v4l devices.
>
> Oh yes, very much agreed!
>
> The library should
>  - provide a single API to access both v4l1 and v4l2
>  - maybe allow non-v4l devices (network cams)
>  - make it easy to get a picture from any detected cam in a
> particular format (and e.g. perform MJPEG decoding or resolution
> rescaling along the way)
>  - provide a standard plug-in API (maybe gstreamer-like) for the
> video stream. This is necessary to support stuff like software
> autofocus for some Logitech webcams, or for turning the picture
> upside down (necessary for some webcams built into notebooks)
>  - extend the plugin API to controls, e.g. allow automatic framerate
> (i.e. shutter speed) selection by user-supplied software as well as
> framerate selection by the webcam's firmware.
>  - provide a standard way for controls like brightness, focus, motor
>    controls. Emulate controls like brightness in software

- standard API to scan for channels (TV & radio), preferably also 
setting a standard config format containing the channel info.
- simple video format conversions for the various YUV/RGB formats.
- storing and retrieving card preferences (e.g. recording volume, 
brightness, MPEG encoder settings, etc.)

The biggest initial problem is deciding how low or high level the 
library will be. I actually think that it might be a good idea to have 
perhaps two libraries: one for low-level stuff (i.e. just a relatively 
thin layer on top of v4l) and a high-level library allowing format 
conversions, etc.

	Hans

>
> The following is a start, but AFAICT nothing has happened WRT an
> implementation (?):
> <http://linuxtv.org/v4lwiki/index.php/V4L2UserspaceLibrary>
>
> This is a start from a different perspective, quite a bit more
> low-level, not enough for many of my requirements above:
> <http://www.quickcamteam.net/software/libwebcam>
>
> Cheers,
>
>   Richard





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