1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_G_PARM: 5 6********************************** 7ioctl VIDIOC_G_PARM, VIDIOC_S_PARM 8********************************** 9 10Name 11==== 12 13VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set streaming parameters 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_G_PARM 19 20``int ioctl(int fd, VIDIOC_G_PARM, v4l2_streamparm *argp)`` 21 22.. c:macro:: VIDIOC_S_PARM 23 24``int ioctl(int fd, VIDIOC_S_PARM, v4l2_streamparm *argp)`` 25 26Arguments 27========= 28 29``fd`` 30 File descriptor returned by :c:func:`open()`. 31 32``argp`` 33 Pointer to struct :c:type:`v4l2_streamparm`. 34 35Description 36=========== 37 38Applications can request a different frame interval. The capture or 39output device will be reconfigured to support the requested frame 40interval if possible. Optionally drivers may choose to skip or 41repeat frames to achieve the requested frame interval. 42 43For stateful encoders (see :ref:`encoder`) this represents the 44frame interval that is typically embedded in the encoded video stream. 45 46Changing the frame interval shall never change the format. Changing the 47format, on the other hand, may change the frame interval. 48 49Further these ioctls can be used to determine the number of buffers used 50internally by a driver in read/write mode. For implications see the 51section discussing the :c:func:`read()` function. 52 53To get and set the streaming parameters applications call the 54:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and 55:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take a 56pointer to a struct :c:type:`v4l2_streamparm` which contains a 57union holding separate parameters for input and output devices. 58 59.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}| 60 61.. c:type:: v4l2_streamparm 62 63.. flat-table:: struct v4l2_streamparm 64 :header-rows: 0 65 :stub-columns: 0 66 :widths: 1 1 2 67 68 * - __u32 69 - ``type`` 70 - The buffer (stream) type, same as struct 71 :c:type:`v4l2_format` ``type``, set by the 72 application. See :c:type:`v4l2_buf_type`. 73 * - union { 74 - ``parm`` 75 * - struct :c:type:`v4l2_captureparm` 76 - ``capture`` 77 - Parameters for capture devices, used when ``type`` is 78 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or 79 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. 80 * - struct :c:type:`v4l2_outputparm` 81 - ``output`` 82 - Parameters for output devices, used when ``type`` is 83 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. 84 * - __u8 85 - ``raw_data``\ [200] 86 - A place holder for future extensions. 87 * - } 88 - 89 90 91.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 92 93.. c:type:: v4l2_captureparm 94 95.. flat-table:: struct v4l2_captureparm 96 :header-rows: 0 97 :stub-columns: 0 98 :widths: 1 1 2 99 100 * - __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 109 the driver, in seconds. 110 * - :cspan:`2` 111 112 This will configure the speed at which the video source (e.g. a sensor) 113 generates video frames. If the speed is fixed, then the driver may 114 choose to skip or repeat frames in order to achieve the requested 115 frame rate. 116 117 For stateful encoders (see :ref:`encoder`) this represents the 118 frame interval that is typically embedded in the encoded video stream. 119 120 Applications store here the desired frame period, drivers return 121 the actual frame period. 122 123 Changing the video standard (also implicitly by switching 124 the video input) may reset this parameter to the nominal frame 125 period. To reset manually applications can just set this field to 126 zero. 127 128 Drivers support this function only when they set the 129 ``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field. 130 * - __u32 131 - ``extendedmode`` 132 - Custom (driver specific) streaming parameters. When unused, 133 applications and drivers must set this field to zero. Applications 134 using this field should check the driver name and version, see 135 :ref:`querycap`. 136 * - __u32 137 - ``readbuffers`` 138 - Applications set this field to the desired number of buffers used 139 internally by the driver in :c:func:`read()` mode. 140 Drivers return the actual number of buffers. When an application 141 requests zero buffers, drivers should just return the current 142 setting rather than the minimum or an error code. For details see 143 :ref:`rw`. 144 * - __u32 145 - ``reserved``\ [4] 146 - Reserved for future extensions. Drivers and applications must set 147 the array to zero. 148 149 150.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 151 152.. c:type:: v4l2_outputparm 153 154.. flat-table:: struct v4l2_outputparm 155 :header-rows: 0 156 :stub-columns: 0 157 :widths: 1 1 2 158 159 * - __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 168 driver, in seconds. 169 * - :cspan:`2` 170 171 The field is intended to repeat frames on the driver side in 172 :c:func:`write()` mode (in streaming mode timestamps 173 can be used to throttle the output), saving I/O bandwidth. 174 175 For stateful encoders (see :ref:`encoder`) this represents the 176 frame interval that is typically embedded in the encoded video stream 177 and it provides a hint to the encoder of the speed at which raw 178 frames are queued up to the encoder. 179 180 Applications store here the desired frame period, drivers return 181 the actual frame period. 182 183 Changing the video standard (also implicitly by switching 184 the video output) may reset this parameter to the nominal frame 185 period. To reset manually applications can just set this field to 186 zero. 187 188 Drivers support this function only when they set the 189 ``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field. 190 * - __u32 191 - ``extendedmode`` 192 - Custom (driver specific) streaming parameters. When unused, 193 applications and drivers must set this field to zero. Applications 194 using this field should check the driver name and version, see 195 :ref:`querycap`. 196 * - __u32 197 - ``writebuffers`` 198 - Applications set this field to the desired number of buffers used 199 internally by the driver in :c:func:`write()` mode. Drivers 200 return the actual number of buffers. When an application requests 201 zero buffers, drivers should just return the current setting 202 rather than the minimum or an error code. For details see 203 :ref:`rw`. 204 * - __u32 205 - ``reserved``\ [4] 206 - Reserved for future extensions. Drivers and applications must set 207 the array to zero. 208 209 210.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 211 212.. _parm-caps: 213 214.. flat-table:: Streaming Parameters Capabilities 215 :header-rows: 0 216 :stub-columns: 0 217 :widths: 3 1 4 218 219 * - ``V4L2_CAP_TIMEPERFRAME`` 220 - 0x1000 221 - The frame period can be modified by setting the ``timeperframe`` 222 field. 223 224 225.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 226 227.. _parm-flags: 228 229.. flat-table:: Capture Parameters Flags 230 :header-rows: 0 231 :stub-columns: 0 232 :widths: 3 1 4 233 234 * - ``V4L2_MODE_HIGHQUALITY`` 235 - 0x0001 236 - High quality imaging mode. High quality mode is intended for still 237 imaging applications. The idea is to get the best possible image 238 quality that the hardware can deliver. It is not defined how the 239 driver writer may achieve that; it will depend on the hardware and 240 the ingenuity of the driver writer. High quality mode is a 241 different mode from the regular motion video capture modes. In 242 high quality mode: 243 244 - The driver may be able to capture higher resolutions than for 245 motion capture. 246 247 - The driver may support fewer pixel formats than motion capture 248 (eg; true color). 249 250 - The driver may capture and arithmetically combine multiple 251 successive fields or frames to remove color edge artifacts and 252 reduce the noise in the video data. 253 254 - The driver may capture images in slices like a scanner in order 255 to handle larger format images than would otherwise be 256 possible. 257 258 - An image capture operation may be significantly slower than 259 motion capture. 260 261 - Moving objects in the image might have excessive motion blur. 262 263 - Capture might only work through the :c:func:`read()` call. 264 265Return Value 266============ 267 268On success 0 is returned, on error -1 and the ``errno`` variable is set 269appropriately. The generic error codes are described at the 270:ref:`Generic Error Codes <gen-errors>` chapter. 271