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Re: Switching input during capture



Hi Mauro,

On Saturday 29 October 2011 00:30:12 Mauro Carvalho Chehab wrote:
> Em 28-10-2011 14:42, Laurent Pinchart escreveu:
> > On Friday 28 October 2011 03:31:53 Gilles Gigan wrote:
> >> Hi,
> >> I would like to know what is the correct way to switch the current
> >> video input during capture on a card with a single BT878 chip and 4
> >> inputs
> >> (http://store.bluecherry.net/products/PV%252d143-%252d-4-port-video-capt
> >> ur e-card-%2830FPS%29-%252d-OEM.html). I tried doing it in two ways: -
> >> using VIDIOC_S_INPUT to change the current input. While this works, the
> >> next captured frame shows video from the old input in its top half and
> >> video from the new input in the bottom half.
> 
> This is is likely easy to fix. The driver has already a logic to prevent
> changing the buffer while in the middle of a buffer filling. I suspect
> that the BKL removal patches might have broken it somewhat, allowing
> things like that. basically, it should be as simple as not allowing
> changing the input at the top half.

This will work optimally only if the input analog signals are synchronized, 
right ? If we switch to a new input right when the frame start, can the first 
frame captured on the new input be corrupted ?

> Please try the enclosed patch.
> 
> Regards,
> Mauro
> 
> -
> 
> bttv: Avoid switching the video input at the top half.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> 
> diff --git a/drivers/media/video/bt8xx/bttv-driver.c
> b/drivers/media/video/bt8xx/bttv-driver.c index 3dd0660..6a3be6f 100644
> --- a/drivers/media/video/bt8xx/bttv-driver.c
> +++ b/drivers/media/video/bt8xx/bttv-driver.c
> @@ -3978,7 +3978,7 @@ bttv_irq_switch_video(struct bttv *btv)
>  	bttv_set_dma(btv, 0);
> 
>  	/* switch input */
> -	if (UNSET != btv->new_input) {
> +	if (! btv->curr.top && UNSET != btv->new_input) {
>  		video_mux(btv,btv->new_input);
>  		btv->new_input = UNSET;
>  	}

-- 
Regards,

Laurent Pinchart
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