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     * - }
88       -
95 .. flat-table:: struct v4l2_captureparm
96     :header-rows:  0
97     :stub-columns: 0
100     * - __u32
101       - ``capability``
102       - See :ref:`parm-caps`.
103     * - __u32
104       - ``capturemode``
105       - Set by drivers and applications, see :ref:`parm-flags`.
106     * - struct :c:type:`v4l2_fract`
107       - ``timeperframe``
108       - This is the desired period between successive frames captured by
110     * - :cspan:`2`
115 	frame rate.
118 	frame interval that is typically embedded in the encoded video stream.
120 	Applications store here the desired frame period, drivers return
121 	the actual frame period.
124 	the video input) may reset this parameter to the nominal frame
130     * - __u32
131       - ``extendedmode``
132       - Custom (driver specific) streaming parameters. When unused,
136     * - __u32
137       - ``readbuffers``
138       - Applications set this field to the desired number of buffers used
140 	Drivers return the actual number of buffers. When an application
144     * - __u32
145       - ``reserved``\ [4]
146       - Reserved for future extensions. Drivers and applications must set
154 .. flat-table:: struct v4l2_outputparm
155     :header-rows:  0
156     :stub-columns: 0
159     * - __u32
160       - ``capability``
161       - See :ref:`parm-caps`.
162     * - __u32
163       - ``outputmode``
164       - Set by drivers and applications, see :ref:`parm-flags`.
165     * - struct :c:type:`v4l2_fract`
166       - ``timeperframe``
167       - This is the desired period between successive frames output by the
169     * - :cspan:`2`
176 	frame interval that is typically embedded in the encoded video stream
180 	Applications store here the desired frame period, drivers return
181 	the actual frame period.
184 	the video output) may reset this parameter to the nominal frame
190     * - __u32
191       - ``extendedmode``
192       - Custom (driver specific) streaming parameters. When unused,
196     * - __u32
197       - ``writebuffers``
198       - Applications set this field to the desired number of buffers used
200 	return the actual number of buffers. When an application requests
204     * - __u32
205       - ``reserved``\ [4]
206       - Reserved for future extensions. Drivers and applications must set
212 .. _parm-caps:
214 .. flat-table:: Streaming Parameters Capabilities
215     :header-rows:  0
216     :stub-columns: 0
219     * - ``V4L2_CAP_TIMEPERFRAME``
220       - 0x1000
221       - The frame period can be modified by setting the ``timeperframe``
227 .. _parm-flags:
229 .. flat-table:: Capture Parameters Flags
230     :header-rows:  0
231     :stub-columns: 0
234     * - ``V4L2_MODE_HIGHQUALITY``
235       - 0x0001
236       - High quality imaging mode. High quality mode is intended for still
244 	-  The driver may be able to capture higher resolutions than for
247 	-  The driver may support fewer pixel formats than motion capture
250 	-  The driver may capture and arithmetically combine multiple
254 	-  The driver may capture images in slices like a scanner in order
258 	-  An image capture operation may be significantly slower than
261 	-  Moving objects in the image might have excessive motion blur.
263 	-  Capture might only work through the :c:func:`read()` call.
268 On success 0 is returned, on error -1 and the ``errno`` variable is set
270 :ref:`Generic Error Codes <gen-errors>` chapter.