Hi,

Hmm, nasty...

On 10/06/2011 01:13 PM, Hans Verkuil wrote:
> Hi Hans!
>
> I've been looking into a problem with libv4l2 that occurs when you change TV
> standard or video preset using VIDIOC_S_STD or VIDIOC_S_DV_PRESET. These calls
> will change the format implicitly (e.g. if the current format is set for PAL
> at 720x576 and you select NTSC, then the format will be reset to 720x480).
>
> However, libv4l2 isn't taking this into account and will keep using the cached
> dest_fmt value. It is easy to reproduce this using qv4l2.
>
> The same problem is likely to occur with S_CROP (haven't tested that yet,
> though): calling S_CROP can also change the format.
>
> To be precise: S_STD and S_DV_PRESET can change both the crop rectangle and
> the format, and S_CROP can change the format.

First of all it would be good to actually document this behavior of
VIDIOC_S_STD or VIDIOC_S_DV_PRESET, the current docs don't mention this at all:
http://linuxtv.org/downloads/v4l-dvb-apis/standard.html

I've attached 2 patches which should make libv4l2 deal with this correctly.
I assume you've a reproducer for this and I would appreciate it if you could test
if these patches actually fix the issue you are seeing.

Regards,

Hans