[linux-dvb] Re: RFC 0.3: MPEG encoding and decoding V4L2/DVB API additions

Hans Verkuil hverkuil at xs4all.nl
Sun Feb 18 18:25:08 CET 2007

On Sunday 18 February 2007 17:54, Mauro Carvalho Chehab wrote:
> > 6) Scaling and positioning of the video
> >
> > The cx23415 can take the MPEG stream and scale it to an arbitrary
> > width and height and position it at anywhere in the TV-out screen.
> > So you can get effects like having the MPEG output to the top left
> > corner and an OSD in the lower right corner.
> >
> > With VIDIOC_S_FMT I can set the width and height, but there is no
> > provision for an x and y coordinate. Can the struct v4l2_pix_format
> > be expanded to include this? It would be the logical place for it.
> > For most devices the x and y would always to 0, so I don't think it
> > would be a problem.
> Hmm... Please correct me if I'm wrong, but does it make sense to use
> non 0 x,y if you don't have the OSD API defined?

Yes, this position is completely independent from the OSD. I can 
position and scale the MPEG output anywhere I like in the 
720x576 'canvas' (for lack of a better word). It has nothing to do with 
the OSD. The OSD has its own positioning, but that is handled through 
the framebuffer device driver.

This positioning is specific to output devices, at least, I can't think 
of a practical use for input devices.



> I suspect that this feature is really interesting with OSD. If so,
> maybe we can discuss it a little later, together with OSD API. For
> example, we may thing on one tv out positioning API, generic enough
> to be used by both mpeg output and osd. Something like:
> struct {
> 	enum  type {
> 		OSD,
> 	}
> 	int	x,y;
> }

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