Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 1 | <title>Common API Elements</title> |
| 2 | |
| 3 | <para>Programming a V4L2 device consists of these |
| 4 | steps:</para> |
| 5 | |
| 6 | <itemizedlist> |
| 7 | <listitem> |
| 8 | <para>Opening the device</para> |
| 9 | </listitem> |
| 10 | <listitem> |
| 11 | <para>Changing device properties, selecting a video and audio |
| 12 | input, video standard, picture brightness a. o.</para> |
| 13 | </listitem> |
| 14 | <listitem> |
| 15 | <para>Negotiating a data format</para> |
| 16 | </listitem> |
| 17 | <listitem> |
| 18 | <para>Negotiating an input/output method</para> |
| 19 | </listitem> |
| 20 | <listitem> |
| 21 | <para>The actual input/output loop</para> |
| 22 | </listitem> |
| 23 | <listitem> |
| 24 | <para>Closing the device</para> |
| 25 | </listitem> |
| 26 | </itemizedlist> |
| 27 | |
| 28 | <para>In practice most steps are optional and can be executed out of |
| 29 | order. It depends on the V4L2 device type, you can read about the |
| 30 | details in <xref linkend="devices" />. In this chapter we will discuss |
| 31 | the basic concepts applicable to all devices.</para> |
| 32 | |
| 33 | <section id="open"> |
| 34 | <title>Opening and Closing Devices</title> |
| 35 | |
| 36 | <section> |
| 37 | <title>Device Naming</title> |
| 38 | |
| 39 | <para>V4L2 drivers are implemented as kernel modules, loaded |
| 40 | manually by the system administrator or automatically when a device is |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 41 | first discovered. The driver modules plug into the "videodev" kernel |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 42 | module. It provides helper functions and a common application |
| 43 | interface specified in this document.</para> |
| 44 | |
| 45 | <para>Each driver thus loaded registers one or more device nodes |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 46 | with major number 81 and a minor number between 0 and 255. Minor numbers |
| 47 | are allocated dynamically unless the kernel is compiled with the kernel |
| 48 | option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers are |
| 49 | allocated in ranges depending on the device node type (video, radio, etc.).</para> |
| 50 | |
| 51 | <para>Many drivers support "video_nr", "radio_nr" or "vbi_nr" |
| 52 | module options to select specific video/radio/vbi node numbers. This allows |
| 53 | the user to request that the device node is named e.g. /dev/video5 instead |
| 54 | of leaving it to chance. When the driver supports multiple devices of the same |
| 55 | type more than one device node number can be assigned, separated by commas: |
| 56 | <informalexample> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 57 | <screen> |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 58 | > modprobe mydriver video_nr=0,1 radio_nr=0,1</screen> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 59 | </informalexample></para> |
| 60 | |
| 61 | <para>In <filename>/etc/modules.conf</filename> this may be |
| 62 | written as: <informalexample> |
| 63 | <screen> |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 64 | options mydriver video_nr=0,1 radio_nr=0,1 |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 65 | </screen> |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 66 | </informalexample> When no device node number is given as module |
| 67 | option the driver supplies a default.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 68 | |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 69 | <para>Normally udev will create the device nodes in /dev automatically |
| 70 | for you. If udev is not installed, then you need to enable the |
| 71 | CONFIG_VIDEO_FIXED_MINOR_RANGES kernel option in order to be able to correctly |
| 72 | relate a minor number to a device node number. I.e., you need to be certain |
| 73 | that minor number 5 maps to device node name video5. With this kernel option |
| 74 | different device types have different minor number ranges. These ranges are |
| 75 | listed in <xref linkend="devices" />. |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 76 | </para> |
| 77 | |
| 78 | <para>The creation of character special files (with |
| 79 | <application>mknod</application>) is a privileged operation and |
| 80 | devices cannot be opened by major and minor number. That means |
| 81 | applications cannot <emphasis>reliable</emphasis> scan for loaded or |
| 82 | installed drivers. The user must enter a device name, or the |
| 83 | application can try the conventional device names.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 84 | </section> |
| 85 | |
| 86 | <section id="related"> |
| 87 | <title>Related Devices</title> |
| 88 | |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 89 | <para>Devices can support several functions. For example |
| 90 | video capturing, VBI capturing and radio support.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 91 | |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 92 | <para>The V4L2 API creates different nodes for each of these functions.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 93 | |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 94 | <para>The V4L2 API was designed with the idea that one device node could support |
| 95 | all functions. However, in practice this never worked: this 'feature' |
| 96 | was never used by applications and many drivers did not support it and if |
| 97 | they did it was certainly never tested. In addition, switching a device |
| 98 | node between different functions only works when using the streaming I/O |
| 99 | API, not with the read()/write() API.</para> |
| 100 | |
| 101 | <para>Today each device node supports just one function.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 102 | |
| 103 | <para>Besides video input or output the hardware may also |
| 104 | support audio sampling or playback. If so, these functions are |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 105 | implemented as ALSA PCM devices with optional ALSA audio mixer |
| 106 | devices.</para> |
| 107 | |
| 108 | <para>One problem with all these devices is that the V4L2 API |
| 109 | makes no provisions to find these related devices. Some really |
| 110 | complex devices use the Media Controller (see <xref linkend="media_controller" />) |
| 111 | which can be used for this purpose. But most drivers do not use it, |
| 112 | and while some code exists that uses sysfs to discover related devices |
| 113 | (see libmedia_dev in the <ulink url="http://git.linuxtv.org/v4l-utils/">v4l-utils</ulink> |
| 114 | git repository), there is no library yet that can provide a single API towards |
| 115 | both Media Controller-based devices and devices that do not use the Media Controller. |
| 116 | If you want to work on this please write to the linux-media mailing list: &v4l-ml;.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 117 | </section> |
| 118 | |
| 119 | <section> |
| 120 | <title>Multiple Opens</title> |
| 121 | |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 122 | <para>V4L2 devices can be opened more than once.<footnote><para> |
| 123 | There are still some old and obscure drivers that have not been updated to |
| 124 | allow for multiple opens. This implies that for such drivers &func-open; can |
| 125 | return an &EBUSY; when the device is already in use.</para></footnote> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 126 | When this is supported by the driver, users can for example start a |
| 127 | "panel" application to change controls like brightness or audio |
| 128 | volume, while another application captures video and audio. In other words, panel |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 129 | applications are comparable to an ALSA audio mixer application. |
| 130 | Just opening a V4L2 device should not change the state of the device.<footnote> |
| 131 | <para>Unfortunately, opening a radio device often switches the state of the |
| 132 | device to radio mode in many drivers. This behavior should be fixed eventually |
| 133 | as it violates the V4L2 specification.</para></footnote></para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 134 | |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 135 | <para>Once an application has allocated the memory buffers needed for |
| 136 | streaming data (by calling the &VIDIOC-REQBUFS; or &VIDIOC-CREATE-BUFS; ioctls, |
| 137 | or implicitly by calling the &func-read; or &func-write; functions) that |
| 138 | application (filehandle) becomes the owner of the device. It is no longer |
| 139 | allowed to make changes that would affect the buffer sizes (e.g. by calling |
| 140 | the &VIDIOC-S-FMT; ioctl) and other applications are no longer allowed to allocate |
| 141 | buffers or start or stop streaming. The &EBUSY; will be returned instead.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 142 | |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 143 | <para>Merely opening a V4L2 device does not grant exclusive |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 144 | access.<footnote> |
| 145 | <para>Drivers could recognize the |
| 146 | <constant>O_EXCL</constant> open flag. Presently this is not required, |
| 147 | so applications cannot know if it really works.</para> |
| 148 | </footnote> Initiating data exchange however assigns the right |
| 149 | to read or write the requested type of data, and to change related |
| 150 | properties, to this file descriptor. Applications can request |
| 151 | additional access privileges using the priority mechanism described in |
| 152 | <xref linkend="app-pri" />.</para> |
| 153 | </section> |
| 154 | |
| 155 | <section> |
| 156 | <title>Shared Data Streams</title> |
| 157 | |
| 158 | <para>V4L2 drivers should not support multiple applications |
| 159 | reading or writing the same data stream on a device by copying |
| 160 | buffers, time multiplexing or similar means. This is better handled by |
Hans Verkuil | 5d5f87b | 2014-02-04 09:55:19 -0300 | [diff] [blame] | 161 | a proxy application in user space.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 162 | </section> |
| 163 | |
| 164 | <section> |
| 165 | <title>Functions</title> |
| 166 | |
| 167 | <para>To open and close V4L2 devices applications use the |
| 168 | &func-open; and &func-close; function, respectively. Devices are |
| 169 | programmed using the &func-ioctl; function as explained in the |
| 170 | following sections.</para> |
| 171 | </section> |
| 172 | </section> |
| 173 | |
| 174 | <section id="querycap"> |
| 175 | <title>Querying Capabilities</title> |
| 176 | |
| 177 | <para>Because V4L2 covers a wide variety of devices not all |
| 178 | aspects of the API are equally applicable to all types of devices. |
| 179 | Furthermore devices of the same type have different capabilities and |
| 180 | this specification permits the omission of a few complicated and less |
| 181 | important parts of the API.</para> |
| 182 | |
| 183 | <para>The &VIDIOC-QUERYCAP; ioctl is available to check if the kernel |
| 184 | device is compatible with this specification, and to query the <link |
| 185 | linkend="devices">functions</link> and <link linkend="io">I/O |
Mauro Carvalho Chehab | c20eb18 | 2011-06-25 14:11:52 -0300 | [diff] [blame] | 186 | methods</link> supported by the device.</para> |
| 187 | |
| 188 | <para>Starting with kernel version 3.1, VIDIOC-QUERYCAP will return the |
| 189 | V4L2 API version used by the driver, with generally matches the Kernel version. |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 190 | There's no need of using &VIDIOC-QUERYCAP; to check if a specific ioctl is |
| 191 | supported, the V4L2 core now returns ENOTTY if a driver doesn't provide |
Mauro Carvalho Chehab | c20eb18 | 2011-06-25 14:11:52 -0300 | [diff] [blame] | 192 | support for an ioctl.</para> |
| 193 | |
| 194 | <para>Other features can be queried |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 195 | by calling the respective ioctl, for example &VIDIOC-ENUMINPUT; |
| 196 | to learn about the number, types and names of video connectors on the |
| 197 | device. Although abstraction is a major objective of this API, the |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 198 | &VIDIOC-QUERYCAP; ioctl also allows driver specific applications to reliably identify |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 199 | the driver.</para> |
| 200 | |
| 201 | <para>All V4L2 drivers must support |
| 202 | <constant>VIDIOC_QUERYCAP</constant>. Applications should always call |
| 203 | this ioctl after opening the device.</para> |
| 204 | </section> |
| 205 | |
| 206 | <section id="app-pri"> |
| 207 | <title>Application Priority</title> |
| 208 | |
| 209 | <para>When multiple applications share a device it may be |
| 210 | desirable to assign them different priorities. Contrary to the |
| 211 | traditional "rm -rf /" school of thought a video recording application |
| 212 | could for example block other applications from changing video |
| 213 | controls or switching the current TV channel. Another objective is to |
| 214 | permit low priority applications working in background, which can be |
| 215 | preempted by user controlled applications and automatically regain |
| 216 | control of the device at a later time.</para> |
| 217 | |
| 218 | <para>Since these features cannot be implemented entirely in user |
| 219 | space V4L2 defines the &VIDIOC-G-PRIORITY; and &VIDIOC-S-PRIORITY; |
| 220 | ioctls to request and query the access priority associate with a file |
| 221 | descriptor. Opening a device assigns a medium priority, compatible |
| 222 | with earlier versions of V4L2 and drivers not supporting these ioctls. |
| 223 | Applications requiring a different priority will usually call |
| 224 | <constant>VIDIOC_S_PRIORITY</constant> after verifying the device with |
| 225 | the &VIDIOC-QUERYCAP; ioctl.</para> |
| 226 | |
| 227 | <para>Ioctls changing driver properties, such as &VIDIOC-S-INPUT;, |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 228 | return an &EBUSY; after another application obtained higher priority.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 229 | </section> |
| 230 | |
| 231 | <section id="video"> |
| 232 | <title>Video Inputs and Outputs</title> |
| 233 | |
| 234 | <para>Video inputs and outputs are physical connectors of a |
| 235 | device. These can be for example RF connectors (antenna/cable), CVBS |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 236 | a.k.a. Composite Video, S-Video or RGB connectors. Video and VBI |
| 237 | capture devices have inputs. Video and VBI output devices have outputs, |
| 238 | at least one each. Radio devices have no video inputs or outputs.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 239 | |
| 240 | <para>To learn about the number and attributes of the |
| 241 | available inputs and outputs applications can enumerate them with the |
| 242 | &VIDIOC-ENUMINPUT; and &VIDIOC-ENUMOUTPUT; ioctl, respectively. The |
| 243 | &v4l2-input; returned by the <constant>VIDIOC_ENUMINPUT</constant> |
| 244 | ioctl also contains signal status information applicable when the |
| 245 | current video input is queried.</para> |
| 246 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 247 | <para>The &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; ioctls return the |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 248 | index of the current video input or output. To select a different |
| 249 | input or output applications call the &VIDIOC-S-INPUT; and |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 250 | &VIDIOC-S-OUTPUT; ioctls. Drivers must implement all the input ioctls |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 251 | when the device has one or more inputs, all the output ioctls when the |
| 252 | device has one or more outputs.</para> |
| 253 | |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 254 | <example> |
| 255 | <title>Information about the current video input</title> |
| 256 | |
| 257 | <programlisting> |
| 258 | &v4l2-input; input; |
| 259 | int index; |
| 260 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 261 | if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &index)) { |
| 262 | perror("VIDIOC_G_INPUT"); |
| 263 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 264 | } |
| 265 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 266 | memset(&input, 0, sizeof(input)); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 267 | input.index = index; |
| 268 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 269 | if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { |
| 270 | perror("VIDIOC_ENUMINPUT"); |
| 271 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 272 | } |
| 273 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 274 | printf("Current input: %s\n", input.name); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 275 | </programlisting> |
| 276 | </example> |
| 277 | |
| 278 | <example> |
| 279 | <title>Switching to the first video input</title> |
| 280 | |
| 281 | <programlisting> |
| 282 | int index; |
| 283 | |
| 284 | index = 0; |
| 285 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 286 | if (-1 == ioctl(fd, &VIDIOC-S-INPUT;, &index)) { |
| 287 | perror("VIDIOC_S_INPUT"); |
| 288 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 289 | } |
| 290 | </programlisting> |
| 291 | </example> |
| 292 | </section> |
| 293 | |
| 294 | <section id="audio"> |
| 295 | <title>Audio Inputs and Outputs</title> |
| 296 | |
| 297 | <para>Audio inputs and outputs are physical connectors of a |
| 298 | device. Video capture devices have inputs, output devices have |
| 299 | outputs, zero or more each. Radio devices have no audio inputs or |
| 300 | outputs. They have exactly one tuner which in fact |
| 301 | <emphasis>is</emphasis> an audio source, but this API associates |
| 302 | tuners with video inputs or outputs only, and radio devices have |
| 303 | none of these.<footnote> |
| 304 | <para>Actually &v4l2-audio; ought to have a |
| 305 | <structfield>tuner</structfield> field like &v4l2-input;, not only |
| 306 | making the API more consistent but also permitting radio devices with |
| 307 | multiple tuners.</para> |
| 308 | </footnote> A connector on a TV card to loop back the received |
| 309 | audio signal to a sound card is not considered an audio output.</para> |
| 310 | |
| 311 | <para>Audio and video inputs and outputs are associated. Selecting |
| 312 | a video source also selects an audio source. This is most evident when |
| 313 | the video and audio source is a tuner. Further audio connectors can |
| 314 | combine with more than one video input or output. Assumed two |
| 315 | composite video inputs and two audio inputs exist, there may be up to |
| 316 | four valid combinations. The relation of video and audio connectors |
| 317 | is defined in the <structfield>audioset</structfield> field of the |
| 318 | respective &v4l2-input; or &v4l2-output;, where each bit represents |
| 319 | the index number, starting at zero, of one audio input or output.</para> |
| 320 | |
| 321 | <para>To learn about the number and attributes of the |
| 322 | available inputs and outputs applications can enumerate them with the |
| 323 | &VIDIOC-ENUMAUDIO; and &VIDIOC-ENUMAUDOUT; ioctl, respectively. The |
| 324 | &v4l2-audio; returned by the <constant>VIDIOC_ENUMAUDIO</constant> ioctl |
| 325 | also contains signal status information applicable when the current |
| 326 | audio input is queried.</para> |
| 327 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 328 | <para>The &VIDIOC-G-AUDIO; and &VIDIOC-G-AUDOUT; ioctls report |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 329 | the current audio input and output, respectively. Note that, unlike |
| 330 | &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; these ioctls return a structure |
| 331 | as <constant>VIDIOC_ENUMAUDIO</constant> and |
| 332 | <constant>VIDIOC_ENUMAUDOUT</constant> do, not just an index.</para> |
| 333 | |
| 334 | <para>To select an audio input and change its properties |
| 335 | applications call the &VIDIOC-S-AUDIO; ioctl. To select an audio |
| 336 | output (which presently has no changeable properties) applications |
| 337 | call the &VIDIOC-S-AUDOUT; ioctl.</para> |
| 338 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 339 | <para>Drivers must implement all audio input ioctls when the device |
| 340 | has multiple selectable audio inputs, all audio output ioctls when the |
| 341 | device has multiple selectable audio outputs. When the device has any |
| 342 | audio inputs or outputs the driver must set the <constant>V4L2_CAP_AUDIO</constant> |
| 343 | flag in the &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 344 | |
| 345 | <example> |
| 346 | <title>Information about the current audio input</title> |
| 347 | |
| 348 | <programlisting> |
| 349 | &v4l2-audio; audio; |
| 350 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 351 | memset(&audio, 0, sizeof(audio)); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 352 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 353 | if (-1 == ioctl(fd, &VIDIOC-G-AUDIO;, &audio)) { |
| 354 | perror("VIDIOC_G_AUDIO"); |
| 355 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 356 | } |
| 357 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 358 | printf("Current input: %s\n", audio.name); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 359 | </programlisting> |
| 360 | </example> |
| 361 | |
| 362 | <example> |
| 363 | <title>Switching to the first audio input</title> |
| 364 | |
| 365 | <programlisting> |
| 366 | &v4l2-audio; audio; |
| 367 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 368 | memset(&audio, 0, sizeof(audio)); /* clear audio.mode, audio.reserved */ |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 369 | |
| 370 | audio.index = 0; |
| 371 | |
Hans Verkuil | 1c656c87 | 2014-01-07 08:17:35 -0300 | [diff] [blame] | 372 | if (-1 == ioctl(fd, &VIDIOC-S-AUDIO;, &audio)) { |
| 373 | perror("VIDIOC_S_AUDIO"); |
| 374 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 375 | } |
| 376 | </programlisting> |
| 377 | </example> |
| 378 | </section> |
| 379 | |
| 380 | <section id="tuner"> |
| 381 | <title>Tuners and Modulators</title> |
| 382 | |
| 383 | <section> |
| 384 | <title>Tuners</title> |
| 385 | |
| 386 | <para>Video input devices can have one or more tuners |
| 387 | demodulating a RF signal. Each tuner is associated with one or more |
| 388 | video inputs, depending on the number of RF connectors on the tuner. |
| 389 | The <structfield>type</structfield> field of the respective |
| 390 | &v4l2-input; returned by the &VIDIOC-ENUMINPUT; ioctl is set to |
| 391 | <constant>V4L2_INPUT_TYPE_TUNER</constant> and its |
| 392 | <structfield>tuner</structfield> field contains the index number of |
| 393 | the tuner.</para> |
| 394 | |
Hans Verkuil | efcf5bd | 2012-05-28 07:42:54 -0300 | [diff] [blame] | 395 | <para>Radio input devices have exactly one tuner with index zero, no |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 396 | video inputs.</para> |
| 397 | |
| 398 | <para>To query and change tuner properties applications use the |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 399 | &VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctls, respectively. The |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 400 | &v4l2-tuner; returned by <constant>VIDIOC_G_TUNER</constant> also |
| 401 | contains signal status information applicable when the tuner of the |
Hans Verkuil | efcf5bd | 2012-05-28 07:42:54 -0300 | [diff] [blame] | 402 | current video or radio input is queried. Note that |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 403 | <constant>VIDIOC_S_TUNER</constant> does not switch the current tuner, |
| 404 | when there is more than one at all. The tuner is solely determined by |
| 405 | the current video input. Drivers must support both ioctls and set the |
| 406 | <constant>V4L2_CAP_TUNER</constant> flag in the &v4l2-capability; |
| 407 | returned by the &VIDIOC-QUERYCAP; ioctl when the device has one or |
| 408 | more tuners.</para> |
| 409 | </section> |
| 410 | |
| 411 | <section> |
| 412 | <title>Modulators</title> |
| 413 | |
| 414 | <para>Video output devices can have one or more modulators, uh, |
| 415 | modulating a video signal for radiation or connection to the antenna |
| 416 | input of a TV set or video recorder. Each modulator is associated with |
| 417 | one or more video outputs, depending on the number of RF connectors on |
| 418 | the modulator. The <structfield>type</structfield> field of the |
| 419 | respective &v4l2-output; returned by the &VIDIOC-ENUMOUTPUT; ioctl is |
| 420 | set to <constant>V4L2_OUTPUT_TYPE_MODULATOR</constant> and its |
| 421 | <structfield>modulator</structfield> field contains the index number |
Hans Verkuil | efcf5bd | 2012-05-28 07:42:54 -0300 | [diff] [blame] | 422 | of the modulator.</para> |
| 423 | |
| 424 | <para>Radio output devices have exactly one modulator with index |
| 425 | zero, no video outputs.</para> |
| 426 | |
| 427 | <para>A video or radio device cannot support both a tuner and a |
| 428 | modulator. Two separate device nodes will have to be used for such |
| 429 | hardware, one that supports the tuner functionality and one that supports |
| 430 | the modulator functionality. The reason is a limitation with the |
| 431 | &VIDIOC-S-FREQUENCY; ioctl where you cannot specify whether the frequency |
| 432 | is for a tuner or a modulator.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 433 | |
| 434 | <para>To query and change modulator properties applications use |
| 435 | the &VIDIOC-G-MODULATOR; and &VIDIOC-S-MODULATOR; ioctl. Note that |
| 436 | <constant>VIDIOC_S_MODULATOR</constant> does not switch the current |
| 437 | modulator, when there is more than one at all. The modulator is solely |
| 438 | determined by the current video output. Drivers must support both |
| 439 | ioctls and set the <constant>V4L2_CAP_MODULATOR</constant> flag in |
| 440 | the &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl when the |
| 441 | device has one or more modulators.</para> |
| 442 | </section> |
| 443 | |
| 444 | <section> |
| 445 | <title>Radio Frequency</title> |
| 446 | |
| 447 | <para>To get and set the tuner or modulator radio frequency |
| 448 | applications use the &VIDIOC-G-FREQUENCY; and &VIDIOC-S-FREQUENCY; |
| 449 | ioctl which both take a pointer to a &v4l2-frequency;. These ioctls |
| 450 | are used for TV and radio devices alike. Drivers must support both |
| 451 | ioctls when the tuner or modulator ioctls are supported, or |
| 452 | when the device is a radio device.</para> |
| 453 | </section> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 454 | </section> |
| 455 | |
| 456 | <section id="standard"> |
| 457 | <title>Video Standards</title> |
| 458 | |
| 459 | <para>Video devices typically support one or more different video |
| 460 | standards or variations of standards. Each video input and output may |
| 461 | support another set of standards. This set is reported by the |
| 462 | <structfield>std</structfield> field of &v4l2-input; and |
| 463 | &v4l2-output; returned by the &VIDIOC-ENUMINPUT; and |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 464 | &VIDIOC-ENUMOUTPUT; ioctls, respectively.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 465 | |
| 466 | <para>V4L2 defines one bit for each analog video standard |
| 467 | currently in use worldwide, and sets aside bits for driver defined |
| 468 | standards, ⪚ hybrid standards to watch NTSC video tapes on PAL TVs |
| 469 | and vice versa. Applications can use the predefined bits to select a |
| 470 | particular standard, although presenting the user a menu of supported |
| 471 | standards is preferred. To enumerate and query the attributes of the |
| 472 | supported standards applications use the &VIDIOC-ENUMSTD; ioctl.</para> |
| 473 | |
| 474 | <para>Many of the defined standards are actually just variations |
| 475 | of a few major standards. The hardware may in fact not distinguish |
| 476 | between them, or do so internal and switch automatically. Therefore |
| 477 | enumerated standards also contain sets of one or more standard |
| 478 | bits.</para> |
| 479 | |
| 480 | <para>Assume a hypothetic tuner capable of demodulating B/PAL, |
| 481 | G/PAL and I/PAL signals. The first enumerated standard is a set of B |
| 482 | and G/PAL, switched automatically depending on the selected radio |
| 483 | frequency in UHF or VHF band. Enumeration gives a "PAL-B/G" or "PAL-I" |
| 484 | choice. Similar a Composite input may collapse standards, enumerating |
| 485 | "PAL-B/G/H/I", "NTSC-M" and "SECAM-D/K".<footnote> |
| 486 | <para>Some users are already confused by technical terms PAL, |
| 487 | NTSC and SECAM. There is no point asking them to distinguish between |
| 488 | B, G, D, or K when the software or hardware can do that |
| 489 | automatically.</para> |
| 490 | </footnote></para> |
| 491 | |
| 492 | <para>To query and select the standard used by the current video |
| 493 | input or output applications call the &VIDIOC-G-STD; and |
| 494 | &VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis> |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 495 | standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the |
| 496 | parameter of all these ioctls is a pointer to a &v4l2-std-id; type |
| 497 | (a standard set), <emphasis>not</emphasis> an index into the standard |
| 498 | enumeration. Drivers must implement all video standard ioctls |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 499 | when the device has one or more video inputs or outputs.</para> |
| 500 | |
Hans Verkuil | d7a11e1 | 2012-09-14 07:39:55 -0300 | [diff] [blame] | 501 | <para>Special rules apply to devices such as USB cameras where the notion of video |
| 502 | standards makes little sense. More generally for any capture or output device |
| 503 | which is: <itemizedlist> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 504 | <listitem> |
| 505 | <para>incapable of capturing fields or frames at the nominal |
| 506 | rate of the video standard, or</para> |
| 507 | </listitem> |
| 508 | <listitem> |
Hans Verkuil | d7a11e1 | 2012-09-14 07:39:55 -0300 | [diff] [blame] | 509 | <para>that does not support the video standard formats at all.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 510 | </listitem> |
| 511 | </itemizedlist> Here the driver shall set the |
| 512 | <structfield>std</structfield> field of &v4l2-input; and &v4l2-output; |
Hans Verkuil | d7a11e1 | 2012-09-14 07:39:55 -0300 | [diff] [blame] | 513 | to zero and the <constant>VIDIOC_G_STD</constant>, |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 514 | <constant>VIDIOC_S_STD</constant>, |
| 515 | <constant>VIDIOC_QUERYSTD</constant> and |
| 516 | <constant>VIDIOC_ENUMSTD</constant> ioctls shall return the |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 517 | &ENOTTY; or the &EINVAL;.</para> |
Hans Verkuil | d7a11e1 | 2012-09-14 07:39:55 -0300 | [diff] [blame] | 518 | <para>Applications can make use of the <xref linkend="input-capabilities" /> and |
| 519 | <xref linkend="output-capabilities"/> flags to determine whether the video standard ioctls |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 520 | can be used with the given input or output.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 521 | |
| 522 | <example> |
| 523 | <title>Information about the current video standard</title> |
| 524 | |
| 525 | <programlisting> |
| 526 | &v4l2-std-id; std_id; |
| 527 | &v4l2-standard; standard; |
| 528 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 529 | if (-1 == ioctl(fd, &VIDIOC-G-STD;, &std_id)) { |
Hans Verkuil | d7a11e1 | 2012-09-14 07:39:55 -0300 | [diff] [blame] | 530 | /* Note when VIDIOC_ENUMSTD always returns ENOTTY this |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 531 | is no video device or it falls under the USB exception, |
Hans Verkuil | d7a11e1 | 2012-09-14 07:39:55 -0300 | [diff] [blame] | 532 | and VIDIOC_G_STD returning ENOTTY is no error. */ |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 533 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 534 | perror("VIDIOC_G_STD"); |
| 535 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 536 | } |
| 537 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 538 | memset(&standard, 0, sizeof(standard)); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 539 | standard.index = 0; |
| 540 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 541 | while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 542 | if (standard.id & std_id) { |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 543 | printf("Current video standard: %s\n", standard.name); |
| 544 | exit(EXIT_SUCCESS); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 545 | } |
| 546 | |
| 547 | standard.index++; |
| 548 | } |
| 549 | |
| 550 | /* EINVAL indicates the end of the enumeration, which cannot be |
| 551 | empty unless this device falls under the USB exception. */ |
| 552 | |
| 553 | if (errno == EINVAL || standard.index == 0) { |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 554 | perror("VIDIOC_ENUMSTD"); |
| 555 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 556 | } |
| 557 | </programlisting> |
| 558 | </example> |
| 559 | |
| 560 | <example> |
| 561 | <title>Listing the video standards supported by the current |
| 562 | input</title> |
| 563 | |
| 564 | <programlisting> |
| 565 | &v4l2-input; input; |
| 566 | &v4l2-standard; standard; |
| 567 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 568 | memset(&input, 0, sizeof(input)); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 569 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 570 | if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { |
| 571 | perror("VIDIOC_G_INPUT"); |
| 572 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 573 | } |
| 574 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 575 | if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { |
| 576 | perror("VIDIOC_ENUM_INPUT"); |
| 577 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 578 | } |
| 579 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 580 | printf("Current input %s supports:\n", input.name); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 581 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 582 | memset(&standard, 0, sizeof(standard)); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 583 | standard.index = 0; |
| 584 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 585 | while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 586 | if (standard.id & input.std) |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 587 | printf("%s\n", standard.name); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 588 | |
| 589 | standard.index++; |
| 590 | } |
| 591 | |
| 592 | /* EINVAL indicates the end of the enumeration, which cannot be |
| 593 | empty unless this device falls under the USB exception. */ |
| 594 | |
| 595 | if (errno != EINVAL || standard.index == 0) { |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 596 | perror("VIDIOC_ENUMSTD"); |
| 597 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 598 | } |
| 599 | </programlisting> |
| 600 | </example> |
| 601 | |
| 602 | <example> |
| 603 | <title>Selecting a new video standard</title> |
| 604 | |
| 605 | <programlisting> |
| 606 | &v4l2-input; input; |
| 607 | &v4l2-std-id; std_id; |
| 608 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 609 | memset(&input, 0, sizeof(input)); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 610 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 611 | if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { |
| 612 | perror("VIDIOC_G_INPUT"); |
| 613 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 614 | } |
| 615 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 616 | if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { |
| 617 | perror("VIDIOC_ENUM_INPUT"); |
| 618 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 619 | } |
| 620 | |
| 621 | if (0 == (input.std & V4L2_STD_PAL_BG)) { |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 622 | fprintf(stderr, "Oops. B/G PAL is not supported.\n"); |
| 623 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 624 | } |
| 625 | |
| 626 | /* Note this is also supposed to work when only B |
| 627 | <emphasis>or</emphasis> G/PAL is supported. */ |
| 628 | |
| 629 | std_id = V4L2_STD_PAL_BG; |
| 630 | |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 631 | if (-1 == ioctl(fd, &VIDIOC-S-STD;, &std_id)) { |
| 632 | perror("VIDIOC_S_STD"); |
| 633 | exit(EXIT_FAILURE); |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 634 | } |
| 635 | </programlisting> |
| 636 | </example> |
Hans Verkuil | 7dcc606 | 2012-05-15 08:04:28 -0300 | [diff] [blame] | 637 | </section> |
Muralidharan Karicheri | 007701e | 2009-12-03 01:13:17 -0300 | [diff] [blame] | 638 | <section id="dv-timings"> |
| 639 | <title>Digital Video (DV) Timings</title> |
| 640 | <para> |
Hans Verkuil | 7dcc606 | 2012-05-15 08:04:28 -0300 | [diff] [blame] | 641 | The video standards discussed so far have been dealing with Analog TV and the |
Muralidharan Karicheri | 007701e | 2009-12-03 01:13:17 -0300 | [diff] [blame] | 642 | corresponding video timings. Today there are many more different hardware interfaces |
| 643 | such as High Definition TV interfaces (HDMI), VGA, DVI connectors etc., that carry |
| 644 | video signals and there is a need to extend the API to select the video timings |
| 645 | for these interfaces. Since it is not possible to extend the &v4l2-std-id; due to |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 646 | the limited bits available, a new set of ioctls was added to set/get video timings at |
| 647 | the input and output.</para> |
| 648 | |
| 649 | <para>These ioctls deal with the detailed digital video timings that define |
| 650 | each video format. This includes parameters such as the active video width and height, |
| 651 | signal polarities, frontporches, backporches, sync widths etc. The <filename>linux/v4l2-dv-timings.h</filename> |
Hans Verkuil | 7dcc606 | 2012-05-15 08:04:28 -0300 | [diff] [blame] | 652 | header can be used to get the timings of the formats in the <xref linkend="cea861" /> and |
| 653 | <xref linkend="vesadmt" /> standards. |
| 654 | </para> |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 655 | |
| 656 | <para>To enumerate and query the attributes of the DV timings supported by a device |
Hans Verkuil | 7dcc606 | 2012-05-15 08:04:28 -0300 | [diff] [blame] | 657 | applications use the &VIDIOC-ENUM-DV-TIMINGS; and &VIDIOC-DV-TIMINGS-CAP; ioctls. |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 658 | To set DV timings for the device applications use the |
Hans Verkuil | 7dcc606 | 2012-05-15 08:04:28 -0300 | [diff] [blame] | 659 | &VIDIOC-S-DV-TIMINGS; ioctl and to get current DV timings they use the |
| 660 | &VIDIOC-G-DV-TIMINGS; ioctl. To detect the DV timings as seen by the video receiver applications |
| 661 | use the &VIDIOC-QUERY-DV-TIMINGS; ioctl.</para> |
Muralidharan Karicheri | 007701e | 2009-12-03 01:13:17 -0300 | [diff] [blame] | 662 | <para>Applications can make use of the <xref linkend="input-capabilities" /> and |
Hans Verkuil | d4d6819 | 2014-01-07 09:39:57 -0300 | [diff] [blame] | 663 | <xref linkend="output-capabilities"/> flags to determine whether the digital video ioctls |
| 664 | can be used with the given input or output.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 665 | </section> |
| 666 | |
| 667 | &sub-controls; |
| 668 | |
| 669 | <section id="format"> |
| 670 | <title>Data Formats</title> |
| 671 | |
| 672 | <section> |
| 673 | <title>Data Format Negotiation</title> |
| 674 | |
| 675 | <para>Different devices exchange different kinds of data with |
| 676 | applications, for example video images, raw or sliced VBI data, RDS |
| 677 | datagrams. Even within one kind many different formats are possible, |
| 678 | in particular an abundance of image formats. Although drivers must |
| 679 | provide a default and the selection persists across closing and |
| 680 | reopening a device, applications should always negotiate a data format |
| 681 | before engaging in data exchange. Negotiation means the application |
| 682 | asks for a particular format and the driver selects and reports the |
| 683 | best the hardware can do to satisfy the request. Of course |
| 684 | applications can also just query the current selection.</para> |
| 685 | |
| 686 | <para>A single mechanism exists to negotiate all data formats |
| 687 | using the aggregate &v4l2-format; and the &VIDIOC-G-FMT; and |
| 688 | &VIDIOC-S-FMT; ioctls. Additionally the &VIDIOC-TRY-FMT; ioctl can be |
| 689 | used to examine what the hardware <emphasis>could</emphasis> do, |
| 690 | without actually selecting a new data format. The data formats |
| 691 | supported by the V4L2 API are covered in the respective device section |
| 692 | in <xref linkend="devices" />. For a closer look at image formats see |
| 693 | <xref linkend="pixfmt" />.</para> |
| 694 | |
| 695 | <para>The <constant>VIDIOC_S_FMT</constant> ioctl is a major |
| 696 | turning-point in the initialization sequence. Prior to this point |
| 697 | multiple panel applications can access the same device concurrently to |
| 698 | select the current input, change controls or modify other properties. |
| 699 | The first <constant>VIDIOC_S_FMT</constant> assigns a logical stream |
| 700 | (video data, VBI data etc.) exclusively to one file descriptor.</para> |
| 701 | |
| 702 | <para>Exclusive means no other application, more precisely no |
| 703 | other file descriptor, can grab this stream or change device |
| 704 | properties inconsistent with the negotiated parameters. A video |
| 705 | standard change for example, when the new standard uses a different |
| 706 | number of scan lines, can invalidate the selected image format. |
| 707 | Therefore only the file descriptor owning the stream can make |
| 708 | invalidating changes. Accordingly multiple file descriptors which |
| 709 | grabbed different logical streams prevent each other from interfering |
| 710 | with their settings. When for example video overlay is about to start |
| 711 | or already in progress, simultaneous video capturing may be restricted |
| 712 | to the same cropping and image size.</para> |
| 713 | |
| 714 | <para>When applications omit the |
| 715 | <constant>VIDIOC_S_FMT</constant> ioctl its locking side effects are |
| 716 | implied by the next step, the selection of an I/O method with the |
| 717 | &VIDIOC-REQBUFS; ioctl or implicit with the first &func-read; or |
| 718 | &func-write; call.</para> |
| 719 | |
| 720 | <para>Generally only one logical stream can be assigned to a |
| 721 | file descriptor, the exception being drivers permitting simultaneous |
| 722 | video capturing and overlay using the same file descriptor for |
| 723 | compatibility with V4L and earlier versions of V4L2. Switching the |
| 724 | logical stream or returning into "panel mode" is possible by closing |
| 725 | and reopening the device. Drivers <emphasis>may</emphasis> support a |
| 726 | switch using <constant>VIDIOC_S_FMT</constant>.</para> |
| 727 | |
| 728 | <para>All drivers exchanging data with |
| 729 | applications must support the <constant>VIDIOC_G_FMT</constant> and |
| 730 | <constant>VIDIOC_S_FMT</constant> ioctl. Implementation of the |
| 731 | <constant>VIDIOC_TRY_FMT</constant> is highly recommended but |
| 732 | optional.</para> |
| 733 | </section> |
| 734 | |
| 735 | <section> |
| 736 | <title>Image Format Enumeration</title> |
| 737 | |
| 738 | <para>Apart of the generic format negotiation functions |
| 739 | a special ioctl to enumerate all image formats supported by video |
| 740 | capture, overlay or output devices is available.<footnote> |
| 741 | <para>Enumerating formats an application has no a-priori |
Mauro Carvalho Chehab | 9aa0885 | 2009-09-15 20:27:18 -0300 | [diff] [blame] | 742 | knowledge of (otherwise it could explicitly ask for them and need not |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 743 | enumerate) seems useless, but there are applications serving as proxy |
| 744 | between drivers and the actual video applications for which this is |
| 745 | useful.</para> |
| 746 | </footnote></para> |
| 747 | |
| 748 | <para>The &VIDIOC-ENUM-FMT; ioctl must be supported |
| 749 | by all drivers exchanging image data with applications.</para> |
| 750 | |
| 751 | <important> |
| 752 | <para>Drivers are not supposed to convert image formats in |
| 753 | kernel space. They must enumerate only formats directly supported by |
| 754 | the hardware. If necessary driver writers should publish an example |
| 755 | conversion routine or library for integration into applications.</para> |
| 756 | </important> |
| 757 | </section> |
| 758 | </section> |
| 759 | |
Pawel Osciak | 53b5d57 | 2011-01-07 01:41:33 -0300 | [diff] [blame] | 760 | &sub-planar-apis; |
| 761 | |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 762 | <section id="crop"> |
| 763 | <title>Image Cropping, Insertion and Scaling</title> |
| 764 | |
| 765 | <para>Some video capture devices can sample a subsection of the |
| 766 | picture and shrink or enlarge it to an image of arbitrary size. We |
| 767 | call these abilities cropping and scaling. Some video output devices |
| 768 | can scale an image up or down and insert it at an arbitrary scan line |
| 769 | and horizontal offset into a video signal.</para> |
| 770 | |
| 771 | <para>Applications can use the following API to select an area in |
| 772 | the video signal, query the default area and the hardware limits. |
| 773 | <emphasis>Despite their name, the &VIDIOC-CROPCAP;, &VIDIOC-G-CROP; |
| 774 | and &VIDIOC-S-CROP; ioctls apply to input as well as output |
| 775 | devices.</emphasis></para> |
| 776 | |
| 777 | <para>Scaling requires a source and a target. On a video capture |
| 778 | or overlay device the source is the video signal, and the cropping |
| 779 | ioctls determine the area actually sampled. The target are images |
| 780 | read by the application or overlaid onto the graphics screen. Their |
| 781 | size (and position for an overlay) is negotiated with the |
| 782 | &VIDIOC-G-FMT; and &VIDIOC-S-FMT; ioctls.</para> |
| 783 | |
| 784 | <para>On a video output device the source are the images passed in |
| 785 | by the application, and their size is again negotiated with the |
| 786 | <constant>VIDIOC_G/S_FMT</constant> ioctls, or may be encoded in a |
| 787 | compressed video stream. The target is the video signal, and the |
| 788 | cropping ioctls determine the area where the images are |
| 789 | inserted.</para> |
| 790 | |
| 791 | <para>Source and target rectangles are defined even if the device |
| 792 | does not support scaling or the <constant>VIDIOC_G/S_CROP</constant> |
| 793 | ioctls. Their size (and position where applicable) will be fixed in |
| 794 | this case. <emphasis>All capture and output device must support the |
| 795 | <constant>VIDIOC_CROPCAP</constant> ioctl such that applications can |
| 796 | determine if scaling takes place.</emphasis></para> |
| 797 | |
| 798 | <section> |
| 799 | <title>Cropping Structures</title> |
| 800 | |
| 801 | <figure id="crop-scale"> |
| 802 | <title>Image Cropping, Insertion and Scaling</title> |
| 803 | <mediaobject> |
| 804 | <imageobject> |
| 805 | <imagedata fileref="crop.pdf" format="PS" /> |
| 806 | </imageobject> |
| 807 | <imageobject> |
| 808 | <imagedata fileref="crop.gif" format="GIF" /> |
| 809 | </imageobject> |
| 810 | <textobject> |
| 811 | <phrase>The cropping, insertion and scaling process</phrase> |
| 812 | </textobject> |
| 813 | </mediaobject> |
| 814 | </figure> |
| 815 | |
| 816 | <para>For capture devices the coordinates of the top left |
| 817 | corner, width and height of the area which can be sampled is given by |
| 818 | the <structfield>bounds</structfield> substructure of the |
| 819 | &v4l2-cropcap; returned by the <constant>VIDIOC_CROPCAP</constant> |
| 820 | ioctl. To support a wide range of hardware this specification does not |
| 821 | define an origin or units. However by convention drivers should |
| 822 | horizontally count unscaled samples relative to 0H (the leading edge |
| 823 | of the horizontal sync pulse, see <xref linkend="vbi-hsync" />). |
| 824 | Vertically ITU-R line |
| 825 | numbers of the first field (<xref linkend="vbi-525" />, <xref |
| 826 | linkend="vbi-625" />), multiplied by two if the driver can capture both |
| 827 | fields.</para> |
| 828 | |
| 829 | <para>The top left corner, width and height of the source |
| 830 | rectangle, that is the area actually sampled, is given by &v4l2-crop; |
| 831 | using the same coordinate system as &v4l2-cropcap;. Applications can |
| 832 | use the <constant>VIDIOC_G_CROP</constant> and |
| 833 | <constant>VIDIOC_S_CROP</constant> ioctls to get and set this |
| 834 | rectangle. It must lie completely within the capture boundaries and |
| 835 | the driver may further adjust the requested size and/or position |
| 836 | according to hardware limitations.</para> |
| 837 | |
| 838 | <para>Each capture device has a default source rectangle, given |
| 839 | by the <structfield>defrect</structfield> substructure of |
| 840 | &v4l2-cropcap;. The center of this rectangle shall align with the |
| 841 | center of the active picture area of the video signal, and cover what |
| 842 | the driver writer considers the complete picture. Drivers shall reset |
| 843 | the source rectangle to the default when the driver is first loaded, |
| 844 | but not later.</para> |
| 845 | |
| 846 | <para>For output devices these structures and ioctls are used |
| 847 | accordingly, defining the <emphasis>target</emphasis> rectangle where |
| 848 | the images will be inserted into the video signal.</para> |
| 849 | |
| 850 | </section> |
| 851 | |
| 852 | <section> |
| 853 | <title>Scaling Adjustments</title> |
| 854 | |
| 855 | <para>Video hardware can have various cropping, insertion and |
| 856 | scaling limitations. It may only scale up or down, support only |
| 857 | discrete scaling factors, or have different scaling abilities in |
| 858 | horizontal and vertical direction. Also it may not support scaling at |
| 859 | all. At the same time the &v4l2-crop; rectangle may have to be |
| 860 | aligned, and both the source and target rectangles may have arbitrary |
| 861 | upper and lower size limits. In particular the maximum |
| 862 | <structfield>width</structfield> and <structfield>height</structfield> |
| 863 | in &v4l2-crop; may be smaller than the |
| 864 | &v4l2-cropcap;.<structfield>bounds</structfield> area. Therefore, as |
| 865 | usual, drivers are expected to adjust the requested parameters and |
| 866 | return the actual values selected.</para> |
| 867 | |
| 868 | <para>Applications can change the source or the target rectangle |
| 869 | first, as they may prefer a particular image size or a certain area in |
| 870 | the video signal. If the driver has to adjust both to satisfy hardware |
| 871 | limitations, the last requested rectangle shall take priority, and the |
| 872 | driver should preferably adjust the opposite one. The &VIDIOC-TRY-FMT; |
| 873 | ioctl however shall not change the driver state and therefore only |
| 874 | adjust the requested rectangle.</para> |
| 875 | |
| 876 | <para>Suppose scaling on a video capture device is restricted to |
| 877 | a factor 1:1 or 2:1 in either direction and the target image size must |
| 878 | be a multiple of 16 × 16 pixels. The source cropping |
| 879 | rectangle is set to defaults, which are also the upper limit in this |
| 880 | example, of 640 × 400 pixels at offset 0, 0. An |
| 881 | application requests an image size of 300 × 225 |
| 882 | pixels, assuming video will be scaled down from the "full picture" |
| 883 | accordingly. The driver sets the image size to the closest possible |
| 884 | values 304 × 224, then chooses the cropping rectangle |
| 885 | closest to the requested size, that is 608 × 224 |
| 886 | (224 × 2:1 would exceed the limit 400). The offset |
| 887 | 0, 0 is still valid, thus unmodified. Given the default cropping |
| 888 | rectangle reported by <constant>VIDIOC_CROPCAP</constant> the |
| 889 | application can easily propose another offset to center the cropping |
| 890 | rectangle.</para> |
| 891 | |
| 892 | <para>Now the application may insist on covering an area using a |
| 893 | picture aspect ratio closer to the original request, so it asks for a |
| 894 | cropping rectangle of 608 × 456 pixels. The present |
| 895 | scaling factors limit cropping to 640 × 384, so the |
| 896 | driver returns the cropping size 608 × 384 and adjusts |
| 897 | the image size to closest possible 304 × 192.</para> |
| 898 | |
| 899 | </section> |
| 900 | |
| 901 | <section> |
| 902 | <title>Examples</title> |
| 903 | |
| 904 | <para>Source and target rectangles shall remain unchanged across |
| 905 | closing and reopening a device, such that piping data into or out of a |
| 906 | device will work without special preparations. More advanced |
| 907 | applications should ensure the parameters are suitable before starting |
| 908 | I/O.</para> |
| 909 | |
| 910 | <example> |
| 911 | <title>Resetting the cropping parameters</title> |
| 912 | |
| 913 | <para>(A video capture device is assumed; change |
| 914 | <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> for other |
| 915 | devices.)</para> |
| 916 | |
| 917 | <programlisting> |
| 918 | &v4l2-cropcap; cropcap; |
| 919 | &v4l2-crop; crop; |
| 920 | |
| 921 | memset (&cropcap, 0, sizeof (cropcap)); |
| 922 | cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; |
| 923 | |
| 924 | if (-1 == ioctl (fd, &VIDIOC-CROPCAP;, &cropcap)) { |
| 925 | perror ("VIDIOC_CROPCAP"); |
| 926 | exit (EXIT_FAILURE); |
| 927 | } |
| 928 | |
| 929 | memset (&crop, 0, sizeof (crop)); |
| 930 | crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; |
| 931 | crop.c = cropcap.defrect; |
| 932 | |
| 933 | /* Ignore if cropping is not supported (EINVAL). */ |
| 934 | |
| 935 | if (-1 == ioctl (fd, &VIDIOC-S-CROP;, &crop) |
| 936 | && errno != EINVAL) { |
| 937 | perror ("VIDIOC_S_CROP"); |
| 938 | exit (EXIT_FAILURE); |
| 939 | } |
| 940 | </programlisting> |
| 941 | </example> |
| 942 | |
| 943 | <example> |
| 944 | <title>Simple downscaling</title> |
| 945 | |
| 946 | <para>(A video capture device is assumed.)</para> |
| 947 | |
| 948 | <programlisting> |
| 949 | &v4l2-cropcap; cropcap; |
| 950 | &v4l2-format; format; |
| 951 | |
| 952 | reset_cropping_parameters (); |
| 953 | |
| 954 | /* Scale down to 1/4 size of full picture. */ |
| 955 | |
| 956 | memset (&format, 0, sizeof (format)); /* defaults */ |
| 957 | |
| 958 | format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; |
| 959 | |
| 960 | format.fmt.pix.width = cropcap.defrect.width >> 1; |
| 961 | format.fmt.pix.height = cropcap.defrect.height >> 1; |
| 962 | format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV; |
| 963 | |
| 964 | if (-1 == ioctl (fd, &VIDIOC-S-FMT;, &format)) { |
| 965 | perror ("VIDIOC_S_FORMAT"); |
| 966 | exit (EXIT_FAILURE); |
| 967 | } |
| 968 | |
| 969 | /* We could check the actual image size now, the actual scaling factor |
| 970 | or if the driver can scale at all. */ |
| 971 | </programlisting> |
| 972 | </example> |
| 973 | |
| 974 | <example> |
| 975 | <title>Selecting an output area</title> |
| 976 | |
| 977 | <programlisting> |
| 978 | &v4l2-cropcap; cropcap; |
| 979 | &v4l2-crop; crop; |
| 980 | |
| 981 | memset (&cropcap, 0, sizeof (cropcap)); |
| 982 | cropcap.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; |
| 983 | |
| 984 | if (-1 == ioctl (fd, VIDIOC_CROPCAP;, &cropcap)) { |
| 985 | perror ("VIDIOC_CROPCAP"); |
| 986 | exit (EXIT_FAILURE); |
| 987 | } |
| 988 | |
| 989 | memset (&crop, 0, sizeof (crop)); |
| 990 | |
| 991 | crop.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; |
| 992 | crop.c = cropcap.defrect; |
| 993 | |
| 994 | /* Scale the width and height to 50 % of their original size |
| 995 | and center the output. */ |
| 996 | |
| 997 | crop.c.width /= 2; |
| 998 | crop.c.height /= 2; |
| 999 | crop.c.left += crop.c.width / 2; |
| 1000 | crop.c.top += crop.c.height / 2; |
| 1001 | |
| 1002 | /* Ignore if cropping is not supported (EINVAL). */ |
| 1003 | |
| 1004 | if (-1 == ioctl (fd, VIDIOC_S_CROP, &crop) |
| 1005 | && errno != EINVAL) { |
| 1006 | perror ("VIDIOC_S_CROP"); |
| 1007 | exit (EXIT_FAILURE); |
| 1008 | } |
| 1009 | </programlisting> |
| 1010 | </example> |
| 1011 | |
| 1012 | <example> |
| 1013 | <title>Current scaling factor and pixel aspect</title> |
| 1014 | |
| 1015 | <para>(A video capture device is assumed.)</para> |
| 1016 | |
| 1017 | <programlisting> |
| 1018 | &v4l2-cropcap; cropcap; |
| 1019 | &v4l2-crop; crop; |
| 1020 | &v4l2-format; format; |
| 1021 | double hscale, vscale; |
| 1022 | double aspect; |
| 1023 | int dwidth, dheight; |
| 1024 | |
| 1025 | memset (&cropcap, 0, sizeof (cropcap)); |
| 1026 | cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; |
| 1027 | |
| 1028 | if (-1 == ioctl (fd, &VIDIOC-CROPCAP;, &cropcap)) { |
| 1029 | perror ("VIDIOC_CROPCAP"); |
| 1030 | exit (EXIT_FAILURE); |
| 1031 | } |
| 1032 | |
| 1033 | memset (&crop, 0, sizeof (crop)); |
| 1034 | crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; |
| 1035 | |
| 1036 | if (-1 == ioctl (fd, &VIDIOC-G-CROP;, &crop)) { |
| 1037 | if (errno != EINVAL) { |
| 1038 | perror ("VIDIOC_G_CROP"); |
| 1039 | exit (EXIT_FAILURE); |
| 1040 | } |
| 1041 | |
| 1042 | /* Cropping not supported. */ |
| 1043 | crop.c = cropcap.defrect; |
| 1044 | } |
| 1045 | |
| 1046 | memset (&format, 0, sizeof (format)); |
| 1047 | format.fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; |
| 1048 | |
| 1049 | if (-1 == ioctl (fd, &VIDIOC-G-FMT;, &format)) { |
| 1050 | perror ("VIDIOC_G_FMT"); |
| 1051 | exit (EXIT_FAILURE); |
| 1052 | } |
| 1053 | |
| 1054 | /* The scaling applied by the driver. */ |
| 1055 | |
| 1056 | hscale = format.fmt.pix.width / (double) crop.c.width; |
| 1057 | vscale = format.fmt.pix.height / (double) crop.c.height; |
| 1058 | |
| 1059 | aspect = cropcap.pixelaspect.numerator / |
| 1060 | (double) cropcap.pixelaspect.denominator; |
| 1061 | aspect = aspect * hscale / vscale; |
| 1062 | |
| 1063 | /* Devices following ITU-R BT.601 do not capture |
| 1064 | square pixels. For playback on a computer monitor |
| 1065 | we should scale the images to this size. */ |
| 1066 | |
| 1067 | dwidth = format.fmt.pix.width / aspect; |
| 1068 | dheight = format.fmt.pix.height; |
| 1069 | </programlisting> |
| 1070 | </example> |
| 1071 | </section> |
| 1072 | </section> |
| 1073 | |
Tomasz Stanislawski | 8af4922 | 2011-08-19 07:00:04 -0300 | [diff] [blame] | 1074 | &sub-selection-api; |
| 1075 | |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 1076 | <section id="streaming-par"> |
| 1077 | <title>Streaming Parameters</title> |
| 1078 | |
| 1079 | <para>Streaming parameters are intended to optimize the video |
| 1080 | capture process as well as I/O. Presently applications can request a |
| 1081 | high quality capture mode with the &VIDIOC-S-PARM; ioctl.</para> |
| 1082 | |
| 1083 | <para>The current video standard determines a nominal number of |
| 1084 | frames per second. If less than this number of frames is to be |
| 1085 | captured or output, applications can request frame skipping or |
| 1086 | duplicating on the driver side. This is especially useful when using |
| 1087 | the &func-read; or &func-write;, which are not augmented by timestamps |
Daniel Mack | 3ad2f3fb | 2010-02-03 08:01:28 +0800 | [diff] [blame] | 1088 | or sequence counters, and to avoid unnecessary data copying.</para> |
Mauro Carvalho Chehab | 8e080c2e | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 1089 | |
| 1090 | <para>Finally these ioctls can be used to determine the number of |
| 1091 | buffers used internally by a driver in read/write mode. For |
| 1092 | implications see the section discussing the &func-read; |
| 1093 | function.</para> |
| 1094 | |
| 1095 | <para>To get and set the streaming parameters applications call |
| 1096 | the &VIDIOC-G-PARM; and &VIDIOC-S-PARM; ioctl, respectively. They take |
| 1097 | a pointer to a &v4l2-streamparm;, which contains a union holding |
| 1098 | separate parameters for input and output devices.</para> |
| 1099 | |
| 1100 | <para>These ioctls are optional, drivers need not implement |
| 1101 | them. If so, they return the &EINVAL;.</para> |
| 1102 | </section> |