ioctl VIDIOC_QUERYCAP

&manvol;

VIDIOC_QUERYCAP

Query device capabilities

    	int ioctl
    	int fd
    	int request
    	struct v4l2_capability *argp

## Arguments

`fd`

- &fd;

`request`

- VIDIOC_QUERYCAP

`argp`

## Description

All V4L2 devices support the `VIDIOC_QUERYCAP` ioctl. It is used to identify kernel devices compatible with this specification and to obtain information about driver and hardware capabilities. The ioctl takes a pointer to a &v4l2-capability; which is filled by the driver. When the driver is not compatible with this specification the ioctl returns an &EINVAL;.

## struct v4l2_capability

&cs-str;
__u8 | driver[16] | Name of the driver, a unique NUL-terminated ASCII string. For example: "bttv". Driver specific applications can use this information to verify the driver identity. It is also useful to work around known bugs, or to identify drivers in error reports. Storing strings in fixed sized arrays is bad practice but unavoidable here. Drivers and applications should take precautions to never read or write beyond the end of the array and to make sure the strings are properly NUL-terminated.
__u8 | card[32] | Name of the device, a NUL-terminated ASCII string. For example: "Yoyodyne TV/FM". One driver may support different brands or models of video hardware. This information is intended for users, for example in a menu of available devices. Since multiple TV cards of the same brand may be installed which are supported by the same driver, this name should be combined with the character device file name (⪚ `/dev/video2`) or the bus_info string to avoid ambiguities.
__u8 | bus_info[32] | Location of the device in the system, a NUL-terminated ASCII string. For example: "PCI Slot 4". This information is intended for users, to distinguish multiple identical devices. If no such information is available the field may simply count the devices controlled by the driver, or contain the empty string (bus_info[0] = 0).
__u32 | version | Version number of the driver. Starting on kernel 3.1, the version reported is provided per V4L2 subsystem, following the same Kernel numberation scheme. However, it should not always return the same version as the kernel, if, for example, an stable or distribution-modified kernel uses the V4L2 stack from a newer kernel. The version number is formatted using the `KERNEL_VERSION()` macro:
    #define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))

    __u32 version = KERNEL_VERSION(0, 8, 1);

    printf ("Version: %u.%u.%u\n",
    	(version >> 16) & 0xFF,
    	(version >> 8) & 0xFF,
    	 version & 0xFF);
__u32 | capabilities | Device capabilities, see device-capabilities.
__u32 | reserved[4] | Reserved for future extensions. Drivers must set this array to zero.

## Device Capabilities Flags

&cs-def;
`V4L2_CAP_VIDEO_CAPTURE` | 0x00000001 | The device supports the single-planar API through the Video Capture interface.
`V4L2_CAP_VIDEO_CAPTURE_MPLANE` | 0x00001000 | The device supports the multi-planar API through the Video Capture interface.
`V4L2_CAP_VIDEO_OUTPUT` | 0x00000002 | The device supports the single-planar API through the Video Output interface.
`V4L2_CAP_VIDEO_OUTPUT_MPLANE` | 0x00002000 | The device supports the multi-planar API through the Video Output interface.
`V4L2_CAP_VIDEO_OVERLAY` | 0x00000004 | The device supports the Video Overlay interface. A video overlay device typically stores captured images directly in the video memory of a graphics card, with hardware clipping and scaling.
`V4L2_CAP_VBI_CAPTURE` | 0x00000010 | The device supports the Raw VBI Capture interface, providing Teletext and Closed Caption data.
`V4L2_CAP_VBI_OUTPUT` | 0x00000020 | The device supports the Raw VBI Output interface.
`V4L2_CAP_SLICED_VBI_CAPTURE` | 0x00000040 | The device supports the Sliced VBI Capture interface.
`V4L2_CAP_SLICED_VBI_OUTPUT` | 0x00000080 | The device supports the Sliced VBI Output interface.
`V4L2_CAP_RDS_CAPTURE` | 0x00000100 | The device supports the RDS capture interface.
`V4L2_CAP_VIDEO_OUTPUT_OVERLAY` | 0x00000200 | The device supports the Video Output Overlay (OSD) interface. Unlike the Video Overlay interface, this is a secondary function of video output devices and overlays an image onto an outgoing video signal. When the driver sets this flag, it must clear the `V4L2_CAP_VIDEO_OVERLAY` flag and vice versa. The &v4l2-framebuffer; lacks an &v4l2-buf-type; field, therefore the type of overlay is implied by the driver capabilities.
`V4L2_CAP_HW_FREQ_SEEK` | 0x00000400 | The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for hardware frequency seeking.
`V4L2_CAP_RDS_OUTPUT` | 0x00000800 | The device supports the RDS output interface.
`V4L2_CAP_TUNER` | 0x00010000 | The device has some sort of tuner to receive RF-modulated video signals. For more information about tuner programming see tuner.
`V4L2_CAP_AUDIO` | 0x00020000 | The device has audio inputs or outputs. It may or may not support audio recording or playback, in PCM or compressed formats. PCM audio support must be implemented as ALSA or OSS interface. For more information on audio inputs and outputs see audio.
`V4L2_CAP_RADIO` | 0x00040000 | This is a radio receiver.
`V4L2_CAP_MODULATOR` | 0x00080000 | The device has some sort of modulator to emit RF-modulated video/audio signals. For more information about modulator programming see tuner.
`V4L2_CAP_READWRITE` | 0x01000000 | The device supports the read() and/or write() I/O methods.
`V4L2_CAP_ASYNCIO` | 0x02000000 | The device supports the asynchronous I/O methods.
`V4L2_CAP_STREAMING` | 0x04000000 | The device supports the streaming I/O method.

&return-value;