Hi,
On 10/07/2011 11:06 AM, Hans Verkuil wrote:
On Friday 07 October 2011 09:57:42 Hans de Goede wrote:
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
Odd, I'd have sworn that it was in the docs.
The full list of ioctls that can change both the crop settings and the format
is:
VIDIOC_S_STD
VIDIOC_S_DV_PRESET
The patch already handles these 2 :)
VIDIOC_S_DV_TIMINGS
VIDIOC_S_INPUT (can implicitly change standard/preset)
I'll add these 2.
VIDIOC_S_OUTPUT (ditto)
libv4l2 only cares about capture, all the rest it just passes
through completely unmodified.
VIDIOC_S_CROP
Hmm, can this also change the fmt? That would be an unexpected
side effect. But if it does I can handle it the same way, right?
Note that I suspect that there are quite a few drivers that do not handle this
correctly. After all, for normal SDTV capture cards you almost never change
the TV standard once it is set up at the start so I doubt if this has been
tested much. For DV_PRESET it is much more common to switch from e.g.
720p to 1080p. That is how I found this issue.
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.
Almost working. The second patch forgot to set src_fmt.type, so I got an error
back. After initializing it to BUF_TYPE_VIDEO_CAPTURE it worked fine.
Thanks for testing, and duh wrt my G_FMT mistake. If you can answer my question
about S_CROP then I'll go add the other ioctls which need similar handling to
my 2nd patch and push both patches.
Regards,
Hans
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