[linux-dvb] Re: SAA7146 Cropping

[Michael Hunold <hunold@convergence.de>]

Hello Jeremy,

On 07/07/04 17:41, Jeremy Jones wrote:
> I am trying to develop a DVB application which has a PIG (Picture In 
> Graphic) feature common to most DVB-S IRDs.  To achieve this I need to 
> shrink the video down to 1/4th of the screen and place it in the upper 
> right hand corner.  After digging though some documentation it seems 
> that this should be possible using v4l2 API (in fact there is example to 
> do exactly what I'm trying to do 
> http://v4l2spec.bytesex.org/spec-single/v4l2.html#CROP).  When I try to 
> run this example I get an EINVAL error on the VIDIOC_CROPCAP ioctl().  I 
> have a Nexus-S card which has an SAA7146 MPEG decoder so I looked at the 
> saa7146_video.c file and noticed that it doesn't handle this ioctl() 
> which seems to be the cause of the EINVAL error. 
This is correct, the driver does not support the ioctl.

> I looked at the SAA7146 
> documentation and it seems like it should be possible to scale the video 
> output down to 1/4th the screen.
Yes, it's possible, but you're on the wrong track.

> Is there any other way 
> to accomplish what I'm trying to do ?  Am I even using the correct APIs 
> to do what I'm trying to accomplish ?  
I don't think so.

Do you want to compose a "screen" from multiple elements, like live 
video, static graphics and text?

The data from the Video4Linux device is just one of the elements that 
needs to be composed, it's not the underlying screen. So there is no 
need to crop the video data, it just needs to be scaled and positionend 
onto your "screen", ie. you need to specify the correct capture size, 
then capture the data and overlay or copy the data onto your destination 
screen.

> Thank You,
> bball
CU
Michael.