Re: V4L2 API ambiguities: workshop presentation

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On Fri August 17 2012 14:48:23 Hans de Goede wrote:
> Hi,
> 
> On 08/17/2012 12:35 PM, Hans Verkuil wrote:
> > Hi all,
> >
> > I've prepared a presentation for the upcoming workshop based on my RFC and the
> > comments I received.
> >
> > It is available here:
> >
> > http://hverkuil.home.xs4all.nl/presentations/v4l2-workshop-2012.odp
> > http://hverkuil.home.xs4all.nl/presentations/v4l2-workshop-2012.pdf
> >
> > Attendees of the workshop: please review this before the workshop starts. I
> > want to go through this list fairly quickly (particularly slides 1-14) so we
> > can have more time for other topics.
> 
> A note on the Pixel Aspect Ratio from me, since I won't be attending:
> 
> I'm not sure if having a VIDIOC_G_PIXELASPECT is enough, it will work
> to get the current mode, but not for enumerating. Also it will not
> work with TRY_FMT, that is one cannot find out the actual pixelaspect
> until after a S_FMT. As mentioned in previous mail I think at a minimum
> the results of ENUM_FRAMESIZES should contain the pixel aspect per framesize,
> there is enough reserved space in the relevant structs to make this happen

Pixel aspect doesn't belong in the FMT ioctls: the pixel aspect ratio is
a property of the video input/output format, but the FMT ioctls deal with
scaling as well, so the aspect ratio would then be scaled as well, making
it very complex indeed.

Regarding ENUM_FRAMESIZES: it makes sense to add an aspect ratio here for
use with sensors. But for video receivers ENUM_FRAMESIZES isn't applicable.

Regards,

	Hans
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