[MPlayer-dev-eng] [PATCH] Fix inverted colours when capturing YV12 in V4L2 mode

[Luc Gallant]

On 12/16/05, Jindrich Makovicka <makovick at kmlinux.fjfi.cvut.cz> wrote:
> Luc Gallant wrote:
> > Fixes: When capturing YV12 in V4L2 mode, the U and V planes are
> > inverted. This is because code was copied from V4L1, and V4L1 had a
> > problem with some pixel formats Also fixes some formatting switch case
> > entries that were wrong. Details of the YV12 == YVU420 are available
> > here: http://v4l2spec.bytesex.org/spec-single/v4l2.html (search YV12)
> >
> > How to test if it works: Open up a device that sends YV12 video in
> > V4L2, and see if the colours are inverted.
> >
> > In my case, I used my loopback driver (which is known to work with the
> > YV12 format) to ensure that the patch worked.
> > Another way to test is to capture an I420 stream (most capture cards),
> > and play it in YV12 format, and make sure the colours are INVERTED
> > (since i420 is the opposite of YV12)
>
> What card are you using? I suppose it rather always produces YVU420,
> even if it's asked to produce I420/YUV420. The current code works
> without problems on my saa7134. The plane swapping is used since v4l1
> because at least bt8x8 was unable to produce YV12/YVU420 natively.
>

I am using a virtual v4l2 driver that I created (ported from v4l1
actually). I can send in whatever file type I want, and in this case I
send in YV12/YVU420. When I send in that file type, the colours are
inverted. When I send in I420/YUV420 and tell mplayer about this, it
works fine...

It is ok that the bt8x8 was unable to produce YV12/YVU420 natively. In
my opinion, mplayer should try to set an image format, and if the
driver responds with something that it doesn't have that image format,
then too bad. In the way that mplayer is right now, if a device is
actually sending in YV12, it will display inverted, and the user has
to use -of swapuv or something like this.

Like it says in the code in tvi_v4l2.c, "// YV12 uses
VIDEO_PALETTE_YUV420P, but the planes are swapped", this goes back to
V4L1 and the fact that back then YV12 == YUV420P, which is completely
inverted. With V4L2, it is now correct.

Let me know if there are any more issues or something I missed. Thanks.

Luc Gallant