Could somebody explain to me some strange behavior of v4l2_ioctl call?
When a device supports |V4L2_CAP_VIDEO_OUTPUT_MPLANE capability but does
not support ||V4L2_CAP_VIDEO_OUTPUT, the |v4l2_ioctl function converts
VIDIOC_S_FMT ioctl call: for example, when the specified buffer type is
V4L2_BUF_TYPE_VIDEO_OUTPUT, it is changed to
V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE. But the num_planes value is not
checked after the ioctl call, like after VIDIOC_G_FMT ioctl call is
made. Device may change the num_planes value in call, especially since
number of planes is determined by pixelformat. For example, V4L2
distinguishes single-plane variant of YUV420 format
(V4L2_PIX_FMT_YUV420) from multi-plane one (V4L2_PIX_FMT_YUV420M). If
the number of planes is not checked, program may select multi-plane
variant, which will not handle correctly. Shouldn't the library check
the number of planes after ioctl call?
Rafal
