ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT

&manvol;

VIDIOC_G_FMT

VIDIOC_S_FMT

VIDIOC_TRY_FMT

Get or set the data format, try a format

    	int ioctl
    	int fd
    	int request
    	struct v4l2_format
    *argp

## Arguments

`fd`

- &fd;

`request`

- VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT

`argp`

## Description

These ioctls are used to negotiate the format of data (typically image format) exchanged between driver and application.

To query the current parameters applications set the type field of a struct v4l2_format to the respective buffer (stream) type. For example video capture devices use `V4L2_BUF_TYPE_VIDEO_CAPTURE`. When the application calls the `VIDIOC_G_FMT` ioctl with a pointer to this structure the driver fills the respective member of the fmt union. In case of video capture devices that is the &v4l2-pix-format; pix member. When the requested buffer type is not supported drivers return an &EINVAL;.

To change the current format parameters applications initialize the type field and all fields of the respective fmt union member. For details see the documentation of the various devices types in devices. Good practice is to query the current parameters first, and to modify only those parameters not suitable for the application. When the application calls the `VIDIOC_S_FMT` ioctl with a pointer to a v4l2_format structure the driver checks and adjusts the parameters against hardware abilities. Drivers should not return an error code unless the input is ambiguous, this is a mechanism to fathom device capabilities and to approach parameters acceptable for both the application and driver. On success the driver may program the hardware, allocate resources and generally prepare for data exchange. Finally the `VIDIOC_S_FMT` ioctl returns the current format parameters as `VIDIOC_G_FMT` does. Very simple, inflexible devices may even ignore all input and always return the default parameters. However all V4L2 devices exchanging data with the application must implement the `VIDIOC_G_FMT` and `VIDIOC_S_FMT` ioctl. When the requested buffer type is not supported drivers return an &EINVAL; on a `VIDIOC_S_FMT` attempt. When I/O is already in progress or the resource is not available for other reasons drivers return the &EBUSY;.

The `VIDIOC_TRY_FMT` ioctl is equivalent to `VIDIOC_S_FMT` with one exception: it does not change driver state. It can also be called at any time, never returning EBUSY. This function is provided to negotiate parameters, to learn about hardware limitations, without disabling I/O or possibly time consuming hardware preparations. Although strongly recommended drivers are not required to implement this ioctl.

## struct v4l2_format

&v4l2-buf-type; | type |  | Type of the data stream, see v4l2-buf-type.
union | fmt
| &v4l2-pix-format; | pix | Definition of an image format, see pixfmt, used by video capture and output devices.
| &v4l2-window; | win | Definition of an overlaid image, see overlay, used by video overlay devices.
| &v4l2-vbi-format; | vbi | Raw VBI capture or output parameters. This is discussed in more detail in raw-vbi. Used by raw VBI capture and output devices.
| &v4l2-sliced-vbi-format; | sliced | Sliced VBI capture or output parameters. See sliced for details. Used by sliced VBI capture and output devices.
| __u8 | raw_data[200] | Place holder for future extensions and custom (driver defined) formats with type `V4L2_BUF_TYPE_PRIVATE` and higher.

&return-value;

EBUSY

- The data format cannot be changed at this time, for example because I/O is already in progress.

EINVAL

- The &v4l2-format; type field is invalid, the requested buffer type not supported, or `VIDIOC_TRY_FMT` was called and is not supported with this buffer type.