media/v4l/vidioc-g-parm.rst

1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
13 VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set streaming parameters
38 Applications can request a different frame interval. The capture or
39 output device will be reconfigured to support the requested frame
41 repeat frames to achieve the requested frame interval.
44 frame interval that is typically embedded in the encoded video stream.
46 Changing the frame interval shall never change the format. Changing the
47 format, on the other hand, may change the frame interval.
49 Further these ioctls can be used to determine the number of buffers used
63 .. flat-table:: struct v4l2_streamparm
64     :header-rows:  0
65     :stub-columns: 0
68     * - __u32
69       - ``type``
70       - The buffer (stream) type, same as struct
73     * - union {
74       - ``parm``
75     * - struct :c:type:`v4l2_captureparm`
76       - ``capture``
77       - Parameters for capture devices, used when ``type`` is
80     * - struct :c:type:`v4l2_outputparm`
81       - ``output``
82       - Parameters for output devices, used when ``type`` is
84     * - __u8
85       - ``raw_data``\ [200]
86       - A place holder for future extensions.
87     * - }
94 .. flat-table:: struct v4l2_captureparm
95     :header-rows:  0
96     :stub-columns: 0
99     * - __u32
100       - ``capability``
101       - See :ref:`parm-caps`.
102     * - __u32
103       - ``capturemode``
104       - Set by drivers and applications, see :ref:`parm-flags`.
105     * - struct :c:type:`v4l2_fract`
106       - ``timeperframe``
107       - This is the desired period between successive frames captured by
109     * - :cspan:`2`
114 	frame rate.
117 	frame interval that is typically embedded in the encoded video stream.
119 	Applications store here the desired frame period, drivers return
120 	the actual frame period.
123 	the video input) may reset this parameter to the nominal frame
129     * - __u32
130       - ``extendedmode``
131       - Custom (driver specific) streaming parameters. When unused,
135     * - __u32
136       - ``readbuffers``
137       - Applications set this field to the desired number of buffers used
139 	Drivers return the actual number of buffers. When an application
143     * - __u32
144       - ``reserved``\ [4]
145       - Reserved for future extensions. Drivers and applications must set
153 .. flat-table:: struct v4l2_outputparm
154     :header-rows:  0
155     :stub-columns: 0
158     * - __u32
159       - ``capability``
160       - See :ref:`parm-caps`.
161     * - __u32
162       - ``outputmode``
163       - Set by drivers and applications, see :ref:`parm-flags`.
164     * - struct :c:type:`v4l2_fract`
165       - ``timeperframe``
166       - This is the desired period between successive frames output by the
168     * - :cspan:`2`
175 	frame interval that is typically embedded in the encoded video stream
179 	Applications store here the desired frame period, drivers return
180 	the actual frame period.
183 	the video output) may reset this parameter to the nominal frame
189     * - __u32
190       - ``extendedmode``
191       - Custom (driver specific) streaming parameters. When unused,
195     * - __u32
196       - ``writebuffers``
197       - Applications set this field to the desired number of buffers used
199 	return the actual number of buffers. When an application requests
203     * - __u32
204       - ``reserved``\ [4]
205       - Reserved for future extensions. Drivers and applications must set
211 .. _parm-caps:
213 .. flat-table:: Streaming Parameters Capabilities
214     :header-rows:  0
215     :stub-columns: 0
218     * - ``V4L2_CAP_TIMEPERFRAME``
219       - 0x1000
220       - The frame period can be modified by setting the ``timeperframe``
226 .. _parm-flags:
228 .. flat-table:: Capture Parameters Flags
229     :header-rows:  0
230     :stub-columns: 0
233     * - ``V4L2_MODE_HIGHQUALITY``
234       - 0x0001
235       - High quality imaging mode. High quality mode is intended for still
243 	-  The driver may be able to capture higher resolutions than for
246 	-  The driver may support fewer pixel formats than motion capture
249 	-  The driver may capture and arithmetically combine multiple
253 	-  The driver may capture images in slices like a scanner in order
257 	-  An image capture operation may be significantly slower than
260 	-  Moving objects in the image might have excessive motion blur.
262 	-  Capture might only work through the :c:func:`read()` call.
267 On success 0 is returned, on error -1 and the ``errno`` variable is set
269 :ref:`Generic Error Codes <gen-errors>` chapter.