Video inputs and outputs are physical connectors of a device. These can be for example RF connectors (antenna/cable), CVBS a.k.a. Composite Video, S-Video or RGB connectors. Only video and VBI capture devices have inputs, output devices have outputs, at least one each. Radio devices have no video inputs or outputs.

To learn about the number and attributes of the available inputs and outputs applications can enumerate them with the VIDIOC_ENUMINPUT and VIDIOC_ENUMOUTPUT ioctl, respectively. The struct v4l2_input returned by the VIDIOC_ENUMINPUT ioctl also contains signal status information applicable when the current video input is queried.

The VIDIOC_G_INPUT and VIDIOC_G_OUTPUT ioctl return the index of the current video input or output. To select a different input or output applications call the VIDIOC_S_INPUT and VIDIOC_S_OUTPUT ioctl. Drivers must implement all the input ioctls when the device has one or more inputs, all the output ioctls when the device has one or more outputs.

struct v4l2_input input;
int index;

if (-1 == ioctl (fd, VIDIOC_G_INPUT, &index)) {
	perror ("VIDIOC_G_INPUT");
	exit (EXIT_FAILURE);
}

memset (&input, 0, sizeof (input));
input.index = index;

if (-1 == ioctl (fd, VIDIOC_ENUMINPUT, &input)) {
	perror ("VIDIOC_ENUMINPUT");
	exit (EXIT_FAILURE);
}

printf ("Current input: %s\n", input.name);
      

int index;

index = 0;

if (-1 == ioctl (fd, VIDIOC_S_INPUT, &index)) {
	perror ("VIDIOC_S_INPUT");
	exit (EXIT_FAILURE);
}