[MPlayer-dev-eng] [PATCH] Fix regression in v4l2 channel tuning on cx88 cards

Reimar Döffinger Reimar.Doeffinger at gmx.de
Sat Jun 9 12:42:42 CEST 2012

On Sat, Jun 09, 2012 at 12:07:30PM +0200, Jon Doe wrote:
> Can someone have a look at this? It's been bugging me for 4 years.
> Used to work perfectly.

One problem with the patch is that you are changing the behaviour
for all tv:// protocols, not just v4l.
I guess some of them could require the norm to be set every time.
However the most obvious question is: Why not move exactly this code
into the driver?
Why should each single application have to duplicate the "do nothing
when the new norm is the same as the old one" when the driver can
do it trivially and probably more reliably for all of them?
It probably could even be done in the common v4l layer.
Another thing is that the patch does not fix what might
be considered the real bug:
it does not set the picture size at the right point it seems
and neither does it even realize that it changed.

> > The problem is that cx88 based cards will reset the picture size to
> > 320x240 when changing norms, squashing the picture to a quarter size
> > in the top left corner when changing channels in mplayer. The cx8800
> > driver needs to reset the picture size due to a hardware filter
> > recalculation requirement when changing norms. Others have also
> > noticed this problem in the driver, but no comprehensive fix was found
> > - see http://www.mail-archive.com/linux-media@vger.kernel.org/msg00157.html

Besides what I mentioned above, that it could just do nothing at all
when switching to the norm that is already selected, there is also
the obvious question why the driver thinks it a good idea to switch
to the minimum available size per default.

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