7.48. ioctl VIDIOC_QUERYCAP

7.48.1. Name

VIDIOC_QUERYCAP - Query device capabilities

7.48.2. Synopsis

VIDIOC_QUERYCAP

int ioctl(int fd, VIDIOC_QUERYCAP, struct v4l2_capability *argp)

7.48.3. Arguments

fd

File descriptor returned by open().

argp

Pointer to struct v4l2_capability.

7.48.4. 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 struct v4l2_capability which is filled by the driver. When the driver is not compatible with this specification the ioctl returns an EINVAL error code.

type v4l2_capability

struct v4l2_capability

__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 UTF-8 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 (e. g. /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:0000:05:06.0”. This information is intended for users, to distinguish multiple identical devices. If no such information is available the field must simply count the devices controlled by the driver (“platform:vivid-000”). The bus_info must start with “PCI:” for PCI boards, “PCIe:” for PCI Express boards, “usb-” for USB devices, “I2C:” for i2c devices, “ISA:” for ISA devices, “parport” for parallel port devices and “platform:” for platform devices.
__u32	version	Version number of the driver. Starting with kernel 3.1, the version reported is provided by the V4L2 subsystem following the kernel numbering scheme. However, it may not always return the same version as the kernel if, for example, a stable or distribution-modified kernel uses the V4L2 stack from a newer kernel. The version number is formatted using the KERNEL_VERSION() macro. For example if the media stack corresponds to the V4L2 version shipped with Kernel 4.14, it would be equivalent to:
#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c)) __u32 version = KERNEL_VERSION(4, 14, 0); printf ("Version: %u.%u.%u\\n", (version >> 16) & 0xFF, (version >> 8) & 0xFF, version & 0xFF);
__u32	capabilities	Available capabilities of the physical device as a whole, see Device Capabilities Flags. The same physical device can export multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and /dev/radioZ). The capabilities field should contain a union of all capabilities available around the several V4L2 devices exported to userspace. For all those devices the capabilities field returns the same set of capabilities. This allows applications to open just one of the devices (typically the video device) and discover whether video, vbi and/or radio are also supported.
__u32	device_caps	Device capabilities of the opened device, see Device Capabilities Flags. Should contain the available capabilities of that specific device node. So, for example, device_caps of a radio device will only contain radio related capabilities and no video or vbi capabilities. This field is only set if the capabilities field contains the V4L2_CAP_DEVICE_CAPS capability. Only the capabilities field can have the V4L2_CAP_DEVICE_CAPS capability, device_caps will never set V4L2_CAP_DEVICE_CAPS.
__u32	reserved[3]	Reserved for future extensions. Drivers must set this array to zero.

Device Capabilities Flags

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_M2M	0x00008000	The device supports the single-planar API through the Video Memory-To-Memory interface.
V4L2_CAP_VIDEO_M2M_MPLANE	0x00004000	The device supports the multi-planar API through the Video Memory-To-Memory 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. [1]
V4L2_CAP_HW_FREQ_SEEK	0x00000400	The device supports the ioctl 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 Tuners and Modulators.
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 Inputs and Outputs.
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 Tuners and Modulators.
V4L2_CAP_SDR_CAPTURE	0x00100000	The device supports the SDR Capture interface.
V4L2_CAP_EXT_PIX_FORMAT	0x00200000	The device supports the struct v4l2_pix_format extended fields.
V4L2_CAP_SDR_OUTPUT	0x00400000	The device supports the SDR Output interface.
V4L2_CAP_META_CAPTURE	0x00800000	The device supports the Metadata Interface capture interface.
V4L2_CAP_READWRITE	0x01000000	The device supports the read() and/or write() I/O methods.
V4L2_CAP_EDID	0x02000000	The device stores the EDID for a video input, or retrieves the EDID for a video output. It is a standalone EDID device, so no video streaming etc. will take place. For a video input this is typically an eeprom that supports the VESA Enhanced Display Data Channel Standard. It can be something else as well, for example a micro controller. For a video output this is typically read from an external device such as an HDMI splitter accessed by a serial port.
V4L2_CAP_STREAMING	0x04000000	The device supports the streaming I/O method.
V4L2_CAP_META_OUTPUT	0x08000000	The device supports the Metadata Interface output interface.
V4L2_CAP_TOUCH	0x10000000	This is a touch device.
V4L2_CAP_IO_MC	0x20000000	There is only one input and/or output seen from userspace. The whole video topology configuration, including which I/O entity is routed to the input/output, is configured by userspace via the Media Controller. See Part IV - Media Controller API.
V4L2_CAP_DEVICE_CAPS	0x80000000	The driver fills the device_caps field. This capability can only appear in the capabilities field and never in the device_caps field.

7.48.5. Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

[1]

The struct v4l2_framebuffer lacks an enum v4l2_buf_type field, therefore the type of overlay is implied by the driver capabilities.