To query the current video input applications call the
VIDIOC_G_INPUT ioctl with a pointer to an integer
where the driver stores the number of the input, as in the
struct v4l2_input index field. This ioctl will
fail only when there are no video inputs, returning
EINVAL.
To select a video input applications store the number of the
desired input in an integer and call the
VIDIOC_S_INPUT ioctl with a pointer to this
integer. Side effects are possible. For example inputs may support
different video standards, so the driver may implicitly switch the
current standard. It is good practice to select an input before
querying or negotiating any other parameters.
Information about video inputs is available using the
VIDIOC_ENUMINPUT ioctl.