1.. Permission is granted to copy, distribute and/or modify this 2.. document under the terms of the GNU Free Documentation License, 3.. Version 1.1 or any later version published by the Free Software 4.. Foundation, with no Invariant Sections, no Front-Cover Texts 5.. and no Back-Cover Texts. A copy of the license is included at 6.. Documentation/userspace-api/media/fdl-appendix.rst. 7.. 8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections 9 10.. _VIDIOC_G_PARM: 11 12********************************** 13ioctl VIDIOC_G_PARM, VIDIOC_S_PARM 14********************************** 15 16Name 17==== 18 19VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set streaming parameters 20 21 22Synopsis 23======== 24 25.. c:function:: int ioctl( int fd, VIDIOC_G_PARM, v4l2_streamparm *argp ) 26 :name: VIDIOC_G_PARM 27 28.. c:function:: int ioctl( int fd, VIDIOC_S_PARM, v4l2_streamparm *argp ) 29 :name: VIDIOC_S_PARM 30 31 32Arguments 33========= 34 35``fd`` 36 File descriptor returned by :ref:`open() <func-open>`. 37 38``argp`` 39 Pointer to struct :c:type:`v4l2_streamparm`. 40 41 42Description 43=========== 44 45The current video standard determines a nominal number of frames per 46second. If less than this number of frames is to be captured or output, 47applications can request frame skipping or duplicating on the driver 48side. This is especially useful when using the :ref:`read() <func-read>` or 49:ref:`write() <func-write>`, which are not augmented by timestamps or sequence 50counters, and to avoid unnecessary data copying. 51 52Changing the frame interval shall never change the format. Changing the 53format, on the other hand, may change the frame interval. 54 55Further these ioctls can be used to determine the number of buffers used 56internally by a driver in read/write mode. For implications see the 57section discussing the :ref:`read() <func-read>` function. 58 59To get and set the streaming parameters applications call the 60:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take a 61pointer to a struct :c:type:`v4l2_streamparm` which contains a 62union holding separate parameters for input and output devices. 63 64 65.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}| 66 67.. c:type:: v4l2_streamparm 68 69.. flat-table:: struct v4l2_streamparm 70 :header-rows: 0 71 :stub-columns: 0 72 :widths: 1 1 2 73 74 * - __u32 75 - ``type`` 76 - The buffer (stream) type, same as struct 77 :c:type:`v4l2_format` ``type``, set by the 78 application. See :c:type:`v4l2_buf_type`. 79 * - union { 80 - ``parm`` 81 * - struct :c:type:`v4l2_captureparm` 82 - ``capture`` 83 - Parameters for capture devices, used when ``type`` is 84 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or 85 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. 86 * - struct :c:type:`v4l2_outputparm` 87 - ``output`` 88 - Parameters for output devices, used when ``type`` is 89 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. 90 * - __u8 91 - ``raw_data``\ [200] 92 - A place holder for future extensions. 93 * - } 94 - 95 96 97 98.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 99 100.. c:type:: v4l2_captureparm 101 102.. flat-table:: struct v4l2_captureparm 103 :header-rows: 0 104 :stub-columns: 0 105 :widths: 1 1 2 106 107 * - __u32 108 - ``capability`` 109 - See :ref:`parm-caps`. 110 * - __u32 111 - ``capturemode`` 112 - Set by drivers and applications, see :ref:`parm-flags`. 113 * - struct :c:type:`v4l2_fract` 114 - ``timeperframe`` 115 - This is the desired period between successive frames captured by 116 the driver, in seconds. The field is intended to skip frames on 117 the driver side, saving I/O bandwidth. 118 119 Applications store here the desired frame period, drivers return 120 the actual frame period, which must be greater or equal to the 121 nominal frame period determined by the current video standard 122 (struct :c:type:`v4l2_standard` ``frameperiod`` 123 field). 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 :ref:`read() <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. 148 149 150 151.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 152 153.. c:type:: v4l2_outputparm 154 155.. flat-table:: struct v4l2_outputparm 156 :header-rows: 0 157 :stub-columns: 0 158 :widths: 1 1 2 159 160 * - __u32 161 - ``capability`` 162 - See :ref:`parm-caps`. 163 * - __u32 164 - ``outputmode`` 165 - Set by drivers and applications, see :ref:`parm-flags`. 166 * - struct :c:type:`v4l2_fract` 167 - ``timeperframe`` 168 - This is the desired period between successive frames output by the 169 driver, in seconds. 170 * - :cspan:`2` 171 172 The field is intended to repeat frames on the driver side in 173 :ref:`write() <func-write>` mode (in streaming mode timestamps 174 can be used to throttle the output), saving I/O bandwidth. 175 176 Applications store here the desired frame period, drivers return 177 the actual frame period, which must be greater or equal to the 178 nominal frame period determined by the current video standard 179 (struct :c:type:`v4l2_standard` ``frameperiod`` 180 field). Changing the video standard (also implicitly by switching 181 the video output) may reset this parameter to the nominal frame 182 period. To reset manually applications can just set this field to 183 zero. 184 185 Drivers support this function only when they set the 186 ``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field. 187 * - __u32 188 - ``extendedmode`` 189 - Custom (driver specific) streaming parameters. When unused, 190 applications and drivers must set this field to zero. Applications 191 using this field should check the driver name and version, see 192 :ref:`querycap`. 193 * - __u32 194 - ``writebuffers`` 195 - Applications set this field to the desired number of buffers used 196 internally by the driver in :ref:`write() <func-write>` mode. Drivers 197 return the actual number of buffers. When an application requests 198 zero buffers, drivers should just return the current setting 199 rather than the minimum or an error code. For details see 200 :ref:`rw`. 201 * - __u32 202 - ``reserved``\ [4] 203 - Reserved for future extensions. Drivers and applications must set 204 the array to zero. 205 206 207 208.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 209 210.. _parm-caps: 211 212.. flat-table:: Streaming Parameters Capabilities 213 :header-rows: 0 214 :stub-columns: 0 215 :widths: 3 1 4 216 217 * - ``V4L2_CAP_TIMEPERFRAME`` 218 - 0x1000 219 - The frame skipping/repeating controlled by the ``timeperframe`` 220 field is supported. 221 222 223 224.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 225 226.. _parm-flags: 227 228.. flat-table:: Capture Parameters Flags 229 :header-rows: 0 230 :stub-columns: 0 231 :widths: 3 1 4 232 233 * - ``V4L2_MODE_HIGHQUALITY`` 234 - 0x0001 235 - High quality imaging mode. High quality mode is intended for still 236 imaging applications. The idea is to get the best possible image 237 quality that the hardware can deliver. It is not defined how the 238 driver writer may achieve that; it will depend on the hardware and 239 the ingenuity of the driver writer. High quality mode is a 240 different mode from the regular motion video capture modes. In 241 high quality mode: 242 243 - The driver may be able to capture higher resolutions than for 244 motion capture. 245 246 - The driver may support fewer pixel formats than motion capture 247 (eg; true color). 248 249 - The driver may capture and arithmetically combine multiple 250 successive fields or frames to remove color edge artifacts and 251 reduce the noise in the video data. 252 253 - The driver may capture images in slices like a scanner in order 254 to handle larger format images than would otherwise be 255 possible. 256 257 - An image capture operation may be significantly slower than 258 motion capture. 259 260 - Moving objects in the image might have excessive motion blur. 261 262 - Capture might only work through the :ref:`read() <func-read>` call. 263 264 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