1 .. -*- coding: utf-8; mode: rst -*-
12 VIDIOC_QUERYCAP - Query device capabilities
18 .. c:function:: int ioctl( int fd, VIDIOC_QUERYCAP, struct v4l2_capability *argp )
19 :name: VIDIOC_QUERYCAP
26 File descriptor returned by :ref:`open() <func-open>`.
34 All V4L2 devices support the ``VIDIOC_QUERYCAP`` ioctl. It is used to
35 identify kernel devices compatible with this specification and to obtain
36 information about driver and hardware capabilities. The ioctl takes a
37 pointer to a struct :c:type:`v4l2_capability` which is
38 filled by the driver. When the driver is not compatible with this
39 specification the ioctl returns an ``EINVAL`` error code.
42 .. tabularcolumns:: |p{1.5cm}|p{2.5cm}|p{13cm}|
44 .. c:type:: v4l2_capability
46 .. flat-table:: struct v4l2_capability
57 - Name of the driver, a unique NUL-terminated ASCII string. For
58 example: "bttv". Driver specific applications can use this
59 information to verify the driver identity. It is also useful to
60 work around known bugs, or to identify drivers in error reports.
62 Storing strings in fixed sized arrays is bad practice but
63 unavoidable here. Drivers and applications should take precautions
64 to never read or write beyond the end of the array and to make
65 sure the strings are properly NUL-terminated.
73 - Name of the device, a NUL-terminated UTF-8 string. For example:
74 "Yoyodyne TV/FM". One driver may support different brands or
75 models of video hardware. This information is intended for users,
76 for example in a menu of available devices. Since multiple TV
77 cards of the same brand may be installed which are supported by
78 the same driver, this name should be combined with the character
79 device file name (e. g. ``/dev/video2``) or the ``bus_info``
80 string to avoid ambiguities.
88 - Location of the device in the system, a NUL-terminated ASCII
89 string. For example: "PCI:0000:05:06.0". This information is
90 intended for users, to distinguish multiple identical devices. If
91 no such information is available the field must simply count the
92 devices controlled by the driver ("platform:vivi-000"). The
93 bus_info must start with "PCI:" for PCI boards, "PCIe:" for PCI
94 Express boards, "usb-" for USB devices, "I2C:" for i2c devices,
95 "ISA:" for ISA devices, "parport" for parallel port devices and
96 "platform:" for platform devices.
104 - Version number of the driver.
106 Starting with kernel 3.1, the version reported is provided by the
107 V4L2 subsystem following the kernel numbering scheme. However, it
108 may not always return the same version as the kernel if, for
109 example, a stable or distribution-modified kernel uses the V4L2
110 stack from a newer kernel.
112 The version number is formatted using the ``KERNEL_VERSION()``
119 ``#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))``
121 ``__u32 version = KERNEL_VERSION(0, 8, 1);``
123 ``printf ("Version: %u.%u.%u\\n",``
125 ``(version >> 16) & 0xFF, (version >> 8) & 0xFF, version & 0xFF);``
133 - Available capabilities of the physical device as a whole, see
134 :ref:`device-capabilities`. The same physical device can export
135 multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and
136 /dev/radioZ). The ``capabilities`` field should contain a union of
137 all capabilities available around the several V4L2 devices
138 exported to userspace. For all those devices the ``capabilities``
139 field returns the same set of capabilities. This allows
140 applications to open just one of the devices (typically the video
141 device) and discover whether video, vbi and/or radio are also
150 - Device capabilities of the opened device, see
151 :ref:`device-capabilities`. Should contain the available
152 capabilities of that specific device node. So, for example,
153 ``device_caps`` of a radio device will only contain radio related
154 capabilities and no video or vbi capabilities. This field is only
155 set if the ``capabilities`` field contains the
156 ``V4L2_CAP_DEVICE_CAPS`` capability. Only the ``capabilities``
157 field can have the ``V4L2_CAP_DEVICE_CAPS`` capability,
158 ``device_caps`` will never set ``V4L2_CAP_DEVICE_CAPS``.
166 - Reserved for future extensions. Drivers must set this array to
171 .. tabularcolumns:: |p{6cm}|p{2.2cm}|p{8.8cm}|
173 .. _device-capabilities:
175 .. cssclass:: longtable
177 .. flat-table:: Device Capabilities Flags
184 - ``V4L2_CAP_VIDEO_CAPTURE``
188 - The device supports the single-planar API through the
189 :ref:`Video Capture <capture>` interface.
193 - ``V4L2_CAP_VIDEO_CAPTURE_MPLANE``
197 - The device supports the :ref:`multi-planar API <planar-apis>`
198 through the :ref:`Video Capture <capture>` interface.
202 - ``V4L2_CAP_VIDEO_OUTPUT``
206 - The device supports the single-planar API through the
207 :ref:`Video Output <output>` interface.
211 - ``V4L2_CAP_VIDEO_OUTPUT_MPLANE``
215 - The device supports the :ref:`multi-planar API <planar-apis>`
216 through the :ref:`Video Output <output>` interface.
220 - ``V4L2_CAP_VIDEO_M2M``
224 - The device supports the single-planar API through the Video
225 Memory-To-Memory interface.
229 - ``V4L2_CAP_VIDEO_M2M_MPLANE``
233 - The device supports the :ref:`multi-planar API <planar-apis>`
234 through the Video Memory-To-Memory interface.
238 - ``V4L2_CAP_VIDEO_OVERLAY``
242 - The device supports the :ref:`Video Overlay <overlay>`
243 interface. A video overlay device typically stores captured images
244 directly in the video memory of a graphics card, with hardware
245 clipping and scaling.
249 - ``V4L2_CAP_VBI_CAPTURE``
253 - The device supports the :ref:`Raw VBI Capture <raw-vbi>`
254 interface, providing Teletext and Closed Caption data.
258 - ``V4L2_CAP_VBI_OUTPUT``
262 - The device supports the :ref:`Raw VBI Output <raw-vbi>`
267 - ``V4L2_CAP_SLICED_VBI_CAPTURE``
271 - The device supports the :ref:`Sliced VBI Capture <sliced>`
276 - ``V4L2_CAP_SLICED_VBI_OUTPUT``
280 - The device supports the :ref:`Sliced VBI Output <sliced>`
285 - ``V4L2_CAP_RDS_CAPTURE``
289 - The device supports the :ref:`RDS <rds>` capture interface.
293 - ``V4L2_CAP_VIDEO_OUTPUT_OVERLAY``
297 - The device supports the :ref:`Video Output Overlay <osd>` (OSD)
298 interface. Unlike the *Video Overlay* interface, this is a
299 secondary function of video output devices and overlays an image
300 onto an outgoing video signal. When the driver sets this flag, it
301 must clear the ``V4L2_CAP_VIDEO_OVERLAY`` flag and vice
306 - ``V4L2_CAP_HW_FREQ_SEEK``
310 - The device supports the
311 :ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl
312 for hardware frequency seeking.
316 - ``V4L2_CAP_RDS_OUTPUT``
320 - The device supports the :ref:`RDS <rds>` output interface.
328 - The device has some sort of tuner to receive RF-modulated video
329 signals. For more information about tuner programming see
338 - The device has audio inputs or outputs. It may or may not support
339 audio recording or playback, in PCM or compressed formats. PCM
340 audio support must be implemented as ALSA or OSS interface. For
341 more information on audio inputs and outputs see :ref:`audio`.
349 - This is a radio receiver.
353 - ``V4L2_CAP_MODULATOR``
357 - The device has some sort of modulator to emit RF-modulated
358 video/audio signals. For more information about modulator
359 programming see :ref:`tuner`.
363 - ``V4L2_CAP_SDR_CAPTURE``
367 - The device supports the :ref:`SDR Capture <sdr>` interface.
371 - ``V4L2_CAP_EXT_PIX_FORMAT``
375 - The device supports the struct
376 :c:type:`v4l2_pix_format` extended fields.
380 - ``V4L2_CAP_SDR_OUTPUT``
384 - The device supports the :ref:`SDR Output <sdr>` interface.
388 - ``V4L2_CAP_READWRITE``
392 - The device supports the :ref:`read() <rw>` and/or
393 :ref:`write() <rw>` I/O methods.
397 - ``V4L2_CAP_ASYNCIO``
401 - The device supports the :ref:`asynchronous <async>` I/O methods.
405 - ``V4L2_CAP_STREAMING``
409 - The device supports the :ref:`streaming <mmap>` I/O method.
417 - This is a touch device.
421 - ``V4L2_CAP_DEVICE_CAPS``
425 - The driver fills the ``device_caps`` field. This capability can
426 only appear in the ``capabilities`` field and never in the
427 ``device_caps`` field.
433 On success 0 is returned, on error -1 and the ``errno`` variable is set
434 appropriately. The generic error codes are described at the
435 :ref:`Generic Error Codes <gen-errors>` chapter.
438 The struct :c:type:`v4l2_framebuffer` lacks an
439 enum :c:type:`v4l2_buf_type` field, therefore the
440 type of overlay is implied by the driver capabilities.