VIDIOC_QUERYCAP — Query device capabilities
int ioctl( | int fd, |
| int request, | |
struct v4l2_capability *argp); |
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.
Table A.93. 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:vivi-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
|
#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 | Available capabilities of the physical device as a whole, see Table A.94, “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 Table A.94, “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. |
Table A.94. 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 | 0x00004000 | The device supports the single-planar API through the Video Memory-To-Memory interface. |
V4L2_CAP_VIDEO_M2M_MPLANE | 0x00008000 | 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.[a] |
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 the section called “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 the section called “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 the section called “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_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. |
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. |
[a] The struct v4l2_framebuffer lacks an enum v4l2_buf_type field, therefore the type of overlay is implied by the driver capabilities. | ||
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.