libv4l, yuv420 and gspca-stv06xx conversion

["Erik Andrén" <erik.andren@gmail.com>]

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Hi Hans,
I'm trying to get gstreamer and the yuv420 format conversion in
libv4l to play nice with the gspca-stv06xx driver. Currently this is
not working.

The resolution of the vv6410 sensor is 356*292 pixels and the native
format of the camera is V4L2_PIX_FMT_SGRBG8.
This produces a total image size of 103952 bytes which gets page
aligned to 106496.

When requesting to conversion to yuv420 in gstreamer I launch
gst-launch with the following parameters:
gst-launch-0.10 -v v4l2src queue-size=4 ! ffmpegcolorspace ! xvimageink

gstreamer then proceeds with complaining that it received a frame of
 size 155928 bytes but it expected a frame of size 156512 bytes.

The delivered 155928 size seems sane as 155928 / 356 gives 438 and
155928 / 292 gives 534.

Furthermore, the difference between the received size and the
expected size is 584 bytes which is 2x the height.

Anyhow, I hacked libv4l2.c and padded the frame with 584 in order to
acheive the requested 156512 bytes. This worked and yielded the
attached image.

I'm currently at loss what's the root cause of this.

Could the page align interfer somehow with the frame size?
What's the correct image size? The converted image is clearly correct.

Hans,
do you have any ideas on how to further debug this issue?

RGB images work as intended although they need to be whitebalanced.

Thanks,
Erik
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