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1<HTML><HEAD> 1<TITLE>V4L API</TITLE>
2<TITLE>Video4Linux Kernel API Reference v0.1:19990430</TITLE> 2<H1>Video For Linux APIs</H1>
3</HEAD> 3<table border=0>
4<! Revision History: > 4<tr>
5<! 4/30/1999 - Fred Gleason (fredg@wava.com)> 5<td>
6<! Documented extensions for the Radio Data System (RDS) extensions > 6<A HREF=http://www.linuxtv.org/downloads/video4linux/API/V4L1_API.html>
7<BODY bgcolor="#ffffff"> 7V4L original API</a>
8<H3>Devices</H3> 8</td><td>
9Video4Linux provides the following sets of device files. These live on the 9Obsoleted by V4L2 API
10character device formerly known as "/dev/bttv". /dev/bttv should be a 10</td></tr><tr><td>
11symlink to /dev/video0 for most people. 11<A HREF=http://www.linuxtv.org/downloads/video4linux/API/V4L2_API.html>
12<P> 12V4L2 API</a>
13<TABLE> 13</td><td>
14<TR><TH>Device Name</TH><TH>Minor Range</TH><TH>Function</TH> 14Should be used for new projects
15<TR><TD>/dev/video</TD><TD>0-63</TD><TD>Video Capture Interface</TD> 15</td></tr>
16<TR><TD>/dev/radio</TD><TD>64-127</TD><TD>AM/FM Radio Devices</TD> 16</table>
17<TR><TD>/dev/vtx</TD><TD>192-223</TD><TD>Teletext Interface Chips</TD>
18<TR><TD>/dev/vbi</TD><TD>224-239</TD><TD>Raw VBI Data (Intercast/teletext)</TD>
19</TABLE>
20<P>
21Video4Linux programs open and scan the devices to find what they are looking
22for. Capability queries define what each interface supports. The
23described API is only defined for video capture cards. The relevant subset
24applies to radio cards. Teletext interfaces talk the existing VTX API.
25<P>
26<H3>Capability Query Ioctl</H3>
27The <B>VIDIOCGCAP</B> ioctl call is used to obtain the capability
28information for a video device. The <b>struct video_capability</b> object
29passed to the ioctl is completed and returned. It contains the following
30information
31<P>
32<TABLE>
33<TR><TD><b>name[32]</b><TD>Canonical name for this interface</TD>
34<TR><TD><b>type</b><TD>Type of interface</TD>
35<TR><TD><b>channels</b><TD>Number of radio/tv channels if appropriate</TD>
36<TR><TD><b>audios</b><TD>Number of audio devices if appropriate</TD>
37<TR><TD><b>maxwidth</b><TD>Maximum capture width in pixels</TD>
38<TR><TD><b>maxheight</b><TD>Maximum capture height in pixels</TD>
39<TR><TD><b>minwidth</b><TD>Minimum capture width in pixels</TD>
40<TR><TD><b>minheight</b><TD>Minimum capture height in pixels</TD>
41</TABLE>
42<P>
43The type field lists the capability flags for the device. These are
44as follows
45<P>
46<TABLE>
47<TR><TH>Name</TH><TH>Description</TH>
48<TR><TD><b>VID_TYPE_CAPTURE</b><TD>Can capture to memory</TD>
49<TR><TD><b>VID_TYPE_TUNER</b><TD>Has a tuner of some form</TD>
50<TR><TD><b>VID_TYPE_TELETEXT</b><TD>Has teletext capability</TD>
51<TR><TD><b>VID_TYPE_OVERLAY</b><TD>Can overlay its image onto the frame buffer</TD>
52<TR><TD><b>VID_TYPE_CHROMAKEY</b><TD>Overlay is Chromakeyed</TD>
53<TR><TD><b>VID_TYPE_CLIPPING</b><TD>Overlay clipping is supported</TD>
54<TR><TD><b>VID_TYPE_FRAMERAM</b><TD>Overlay overwrites frame buffer memory</TD>
55<TR><TD><b>VID_TYPE_SCALES</b><TD>The hardware supports image scaling</TD>
56<TR><TD><b>VID_TYPE_MONOCHROME</b><TD>Image capture is grey scale only</TD>
57<TR><TD><b>VID_TYPE_SUBCAPTURE</b><TD>Capture can be of only part of the image</TD>
58</TABLE>
59<P>
60The minimum and maximum sizes listed for a capture device do not imply all
61that all height/width ratios or sizes within the range are possible. A
62request to set a size will be honoured by the largest available capture
63size whose capture is no large than the requested rectangle in either
64direction. For example the quickcam has 3 fixed settings.
65<P>
66<H3>Frame Buffer</H3>
67Capture cards that drop data directly onto the frame buffer must be told the
68base address of the frame buffer, its size and organisation. This is a
69privileged ioctl and one that eventually X itself should set.
70<P>
71The <b>VIDIOCSFBUF</b> ioctl sets the frame buffer parameters for a capture
72card. If the card does not do direct writes to the frame buffer then this
73ioctl will be unsupported. The <b>VIDIOCGFBUF</b> ioctl returns the
74currently used parameters. The structure used in both cases is a
75<b>struct video_buffer</b>.
76<P>
77<TABLE>
78<TR><TD><b>void *base</b></TD><TD>Base physical address of the buffer</TD>
79<TR><TD><b>int height</b></TD><TD>Height of the frame buffer</TD>
80<TR><TD><b>int width</b></TD><TD>Width of the frame buffer</TD>
81<TR><TD><b>int depth</b></TD><TD>Depth of the frame buffer</TD>
82<TR><TD><b>int bytesperline</b></TD><TD>Number of bytes of memory between the start of two adjacent lines</TD>
83</TABLE>
84<P>
85Note that these values reflect the physical layout of the frame buffer.
86The visible area may be smaller. In fact under XFree86 this is commonly the
87case. XFree86 DGA can provide the parameters required to set up this ioctl.
88Setting the base address to NULL indicates there is no physical frame buffer
89access.
90<P>
91<H3>Capture Windows</H3>
92The capture area is described by a <b>struct video_window</b>. This defines
93a capture area and the clipping information if relevant. The
94<b>VIDIOCGWIN</b> ioctl recovers the current settings and the
95<b>VIDIOCSWIN</b> sets new values. A successful call to <b>VIDIOCSWIN</b>
96indicates that a suitable set of parameters have been chosen. They do not
97indicate that exactly what was requested was granted. The program should
98call <b>VIDIOCGWIN</b> to check if the nearest match was suitable. The
99<b>struct video_window</b> contains the following fields.
100<P>
101<TABLE>
102<TR><TD><b>x</b><TD>The X co-ordinate specified in X windows format.</TD>
103<TR><TD><b>y</b><TD>The Y co-ordinate specified in X windows format.</TD>
104<TR><TD><b>width</b><TD>The width of the image capture.</TD>
105<TR><TD><b>height</b><TD>The height of the image capture.</TD>
106<TR><TD><b>chromakey</b><TD>A host order RGB32 value for the chroma key.</TD>
107<TR><TD><b>flags</b><TD>Additional capture flags.</TD>
108<TR><TD><b>clips</b><TD>A list of clipping rectangles. <em>(Set only)</em></TD>
109<TR><TD><b>clipcount</b><TD>The number of clipping rectangles. <em>(Set only)</em></TD>
110</TABLE>
111<P>
112Clipping rectangles are passed as an array. Each clip consists of the following
113fields available to the user.
114<P>
115<TABLE>
116<TR><TD><b>x</b></TD><TD>X co-ordinate of rectangle to skip</TD>
117<TR><TD><b>y</b></TD><TD>Y co-ordinate of rectangle to skip</TD>
118<TR><TD><b>width</b></TD><TD>Width of rectangle to skip</TD>
119<TR><TD><b>height</b></TD><TD>Height of rectangle to skip</TD>
120</TABLE>
121<P>
122Merely setting the window does not enable capturing. Overlay capturing
123(i.e. PCI-PCI transfer to the frame buffer of the video card)
124is activated by passing the <b>VIDIOCCAPTURE</b> ioctl a value of 1, and
125disabled by passing it a value of 0.
126<P>
127Some capture devices can capture a subfield of the image they actually see.
128This is indicated when VIDEO_TYPE_SUBCAPTURE is defined.
129The video_capture describes the time and special subfields to capture.
130The video_capture structure contains the following fields.
131<P>
132<TABLE>
133<TR><TD><b>x</b></TD><TD>X co-ordinate of source rectangle to grab</TD>
134<TR><TD><b>y</b></TD><TD>Y co-ordinate of source rectangle to grab</TD>
135<TR><TD><b>width</b></TD><TD>Width of source rectangle to grab</TD>
136<TR><TD><b>height</b></TD><TD>Height of source rectangle to grab</TD>
137<TR><TD><b>decimation</b></TD><TD>Decimation to apply</TD>
138<TR><TD><b>flags</b></TD><TD>Flag settings for grabbing</TD>
139</TABLE>
140The available flags are
141<P>
142<TABLE>
143<TR><TH>Name</TH><TH>Description</TH>
144<TR><TD><b>VIDEO_CAPTURE_ODD</b><TD>Capture only odd frames</TD>
145<TR><TD><b>VIDEO_CAPTURE_EVEN</b><TD>Capture only even frames</TD>
146</TABLE>
147<P>
148<H3>Video Sources</H3>
149Each video4linux video or audio device captures from one or more
150source <b>channels</b>. Each channel can be queries with the
151<b>VDIOCGCHAN</b> ioctl call. Before invoking this function the caller
152must set the channel field to the channel that is being queried. On return
153the <b>struct video_channel</b> is filled in with information about the
154nature of the channel itself.
155<P>
156The <b>VIDIOCSCHAN</b> ioctl takes an integer argument and switches the
157capture to this input. It is not defined whether parameters such as colour
158settings or tuning are maintained across a channel switch. The caller should
159maintain settings as desired for each channel. (This is reasonable as
160different video inputs may have different properties).
161<P>
162The <b>struct video_channel</b> consists of the following
163<P>
164<TABLE>
165<TR><TD><b>channel</b></TD><TD>The channel number</TD>
166<TR><TD><b>name</b></TD><TD>The input name - preferably reflecting the label
167on the card input itself</TD>
168<TR><TD><b>tuners</b></TD><TD>Number of tuners for this input</TD>
169<TR><TD><b>flags</b></TD><TD>Properties the tuner has</TD>
170<TR><TD><b>type</b></TD><TD>Input type (if known)</TD>
171<TR><TD><b>norm</b><TD>The norm for this channel</TD>
172</TABLE>
173<P>
174The flags defined are
175<P>
176<TABLE>
177<TR><TD><b>VIDEO_VC_TUNER</b><TD>Channel has tuners.</TD>
178<TR><TD><b>VIDEO_VC_AUDIO</b><TD>Channel has audio.</TD>
179<TR><TD><b>VIDEO_VC_NORM</b><TD>Channel has norm setting.</TD>
180</TABLE>
181<P>
182The types defined are
183<P>
184<TABLE>
185<TR><TD><b>VIDEO_TYPE_TV</b><TD>The input is a TV input.</TD>
186<TR><TD><b>VIDEO_TYPE_CAMERA</b><TD>The input is a camera.</TD>
187</TABLE>
188<P>
189<H3>Image Properties</H3>
190The image properties of the picture can be queried with the <b>VIDIOCGPICT</b>
191ioctl which fills in a <b>struct video_picture</b>. The <b>VIDIOCSPICT</b>
192ioctl allows values to be changed. All values except for the palette type
193are scaled between 0-65535.
194<P>
195The <b>struct video_picture</b> consists of the following fields
196<P>
197<TABLE>
198<TR><TD><b>brightness</b><TD>Picture brightness</TD>
199<TR><TD><b>hue</b><TD>Picture hue (colour only)</TD>
200<TR><TD><b>colour</b><TD>Picture colour (colour only)</TD>
201<TR><TD><b>contrast</b><TD>Picture contrast</TD>
202<TR><TD><b>whiteness</b><TD>The whiteness (greyscale only)</TD>
203<TR><TD><b>depth</b><TD>The capture depth (may need to match the frame buffer depth)</TD>
204<TR><TD><b>palette</b><TD>Reports the palette that should be used for this image</TD>
205</TABLE>
206<P>
207The following palettes are defined
208<P>
209<TABLE>
210<TR><TD><b>VIDEO_PALETTE_GREY</b><TD>Linear intensity grey scale (255 is brightest).</TD>
211<TR><TD><b>VIDEO_PALETTE_HI240</b><TD>The BT848 8bit colour cube.</TD>
212<TR><TD><b>VIDEO_PALETTE_RGB565</b><TD>RGB565 packed into 16 bit words.</TD>
213<TR><TD><b>VIDEO_PALETTE_RGB555</b><TD>RGV555 packed into 16 bit words, top bit undefined.</TD>
214<TR><TD><b>VIDEO_PALETTE_RGB24</b><TD>RGB888 packed into 24bit words.</TD>
215<TR><TD><b>VIDEO_PALETTE_RGB32</b><TD>RGB888 packed into the low 3 bytes of 32bit words. The top 8bits are undefined.</TD>
216<TR><TD><b>VIDEO_PALETTE_YUV422</b><TD>Video style YUV422 - 8bits packed 4bits Y 2bits U 2bits V</TD>
217<TR><TD><b>VIDEO_PALETTE_YUYV</b><TD>Describe me</TD>
218<TR><TD><b>VIDEO_PALETTE_UYVY</b><TD>Describe me</TD>
219<TR><TD><b>VIDEO_PALETTE_YUV420</b><TD>YUV420 capture</TD>
220<TR><TD><b>VIDEO_PALETTE_YUV411</b><TD>YUV411 capture</TD>
221<TR><TD><b>VIDEO_PALETTE_RAW</b><TD>RAW capture (BT848)</TD>
222<TR><TD><b>VIDEO_PALETTE_YUV422P</b><TD>YUV 4:2:2 Planar</TD>
223<TR><TD><b>VIDEO_PALETTE_YUV411P</b><TD>YUV 4:1:1 Planar</TD>
224</TABLE>
225<P>
226<H3>Tuning</H3>
227Each video input channel can have one or more tuners associated with it. Many
228devices will not have tuners. TV cards and radio cards will have one or more
229tuners attached.
230<P>
231Tuners are described by a <b>struct video_tuner</b> which can be obtained by
232the <b>VIDIOCGTUNER</b> ioctl. Fill in the tuner number in the structure
233then pass the structure to the ioctl to have the data filled in. The
234tuner can be switched using <b>VIDIOCSTUNER</b> which takes an integer argument
235giving the tuner to use. A struct tuner has the following fields
236<P>
237<TABLE>
238<TR><TD><b>tuner</b><TD>Number of the tuner</TD>
239<TR><TD><b>name</b><TD>Canonical name for this tuner (eg FM/AM/TV)</TD>
240<TR><TD><b>rangelow</b><TD>Lowest tunable frequency</TD>
241<TR><TD><b>rangehigh</b><TD>Highest tunable frequency</TD>
242<TR><TD><b>flags</b><TD>Flags describing the tuner</TD>
243<TR><TD><b>mode</b><TD>The video signal mode if relevant</TD>
244<TR><TD><b>signal</b><TD>Signal strength if known - between 0-65535</TD>
245</TABLE>
246<P>
247The following flags exist
248<P>
249<TABLE>
250<TR><TD><b>VIDEO_TUNER_PAL</b><TD>PAL tuning is supported</TD>
251<TR><TD><b>VIDEO_TUNER_NTSC</b><TD>NTSC tuning is supported</TD>
252<TR><TD><b>VIDEO_TUNER_SECAM</b><TD>SECAM tuning is supported</TD>
253<TR><TD><b>VIDEO_TUNER_LOW</b><TD>Frequency is in a lower range</TD>
254<TR><TD><b>VIDEO_TUNER_NORM</b><TD>The norm for this tuner is settable</TD>
255<TR><TD><b>VIDEO_TUNER_STEREO_ON</b><TD>The tuner is seeing stereo audio</TD>
256<TR><TD><b>VIDEO_TUNER_RDS_ON</b><TD>The tuner is seeing a RDS datastream</TD>
257<TR><TD><b>VIDEO_TUNER_MBS_ON</b><TD>The tuner is seeing a MBS datastream</TD>
258</TABLE>
259<P>
260The following modes are defined
261<P>
262<TABLE>
263<TR><TD><b>VIDEO_MODE_PAL</b><TD>The tuner is in PAL mode</TD>
264<TR><TD><b>VIDEO_MODE_NTSC</b><TD>The tuner is in NTSC mode</TD>
265<TR><TD><b>VIDEO_MODE_SECAM</b><TD>The tuner is in SECAM mode</TD>
266<TR><TD><b>VIDEO_MODE_AUTO</b><TD>The tuner auto switches, or mode does not apply</TD>
267</TABLE>
268<P>
269Tuning frequencies are an unsigned 32bit value in 1/16th MHz or if the
270<b>VIDEO_TUNER_LOW</b> flag is set they are in 1/16th KHz. The current
271frequency is obtained as an unsigned long via the <b>VIDIOCGFREQ</b> ioctl and
272set by the <b>VIDIOCSFREQ</b> ioctl.
273<P>
274<H3>Audio</H3>
275TV and Radio devices have one or more audio inputs that may be selected.
276The audio properties are queried by passing a <b>struct video_audio</b> to <b>VIDIOCGAUDIO</b> ioctl. The
277<b>VIDIOCSAUDIO</b> ioctl sets audio properties.
278<P>
279The structure contains the following fields
280<P>
281<TABLE>
282<TR><TD><b>audio</b><TD>The channel number</TD>
283<TR><TD><b>volume</b><TD>The volume level</TD>
284<TR><TD><b>bass</b><TD>The bass level</TD>
285<TR><TD><b>treble</b><TD>The treble level</TD>
286<TR><TD><b>flags</b><TD>Flags describing the audio channel</TD>
287<TR><TD><b>name</b><TD>Canonical name for the audio input</TD>
288<TR><TD><b>mode</b><TD>The mode the audio input is in</TD>
289<TR><TD><b>balance</b><TD>The left/right balance</TD>
290<TR><TD><b>step</b><TD>Actual step used by the hardware</TD>
291</TABLE>
292<P>
293The following flags are defined
294<P>
295<TABLE>
296<TR><TD><b>VIDEO_AUDIO_MUTE</b><TD>The audio is muted</TD>
297<TR><TD><b>VIDEO_AUDIO_MUTABLE</b><TD>Audio muting is supported</TD>
298<TR><TD><b>VIDEO_AUDIO_VOLUME</b><TD>The volume is controllable</TD>
299<TR><TD><b>VIDEO_AUDIO_BASS</b><TD>The bass is controllable</TD>
300<TR><TD><b>VIDEO_AUDIO_TREBLE</b><TD>The treble is controllable</TD>
301<TR><TD><b>VIDEO_AUDIO_BALANCE</b><TD>The balance is controllable</TD>
302</TABLE>
303<P>
304The following decoding modes are defined
305<P>
306<TABLE>
307<TR><TD><b>VIDEO_SOUND_MONO</b><TD>Mono signal</TD>
308<TR><TD><b>VIDEO_SOUND_STEREO</b><TD>Stereo signal (NICAM for TV)</TD>
309<TR><TD><b>VIDEO_SOUND_LANG1</b><TD>European TV alternate language 1</TD>
310<TR><TD><b>VIDEO_SOUND_LANG2</b><TD>European TV alternate language 2</TD>
311</TABLE>
312<P>
313<H3>Reading Images</H3>
314Each call to the <b>read</b> syscall returns the next available image
315from the device. It is up to the caller to set format and size (using
316the VIDIOCSPICT and VIDIOCSWIN ioctls) and then to pass a suitable
317size buffer and length to the function. Not all devices will support
318read operations.
319<P>
320A second way to handle image capture is via the mmap interface if supported.
321To use the mmap interface a user first sets the desired image size and depth
322properties. Next the VIDIOCGMBUF ioctl is issued. This reports the size
323of buffer to mmap and the offset within the buffer for each frame. The
324number of frames supported is device dependent and may only be one.
325<P>
326The video_mbuf structure contains the following fields
327<P>
328<TABLE>
329<TR><TD><b>size</b><TD>The number of bytes to map</TD>
330<TR><TD><b>frames</b><TD>The number of frames</TD>
331<TR><TD><b>offsets</b><TD>The offset of each frame</TD>
332</TABLE>
333<P>
334Once the mmap has been made the VIDIOCMCAPTURE ioctl starts the
335capture to a frame using the format and image size specified in the
336video_mmap (which should match or be below the initial query size).
337When the VIDIOCMCAPTURE ioctl returns the frame is <em>not</em>
338captured yet, the driver just instructed the hardware to start the
339capture. The application has to use the VIDIOCSYNC ioctl to wait
340until the capture of a frame is finished. VIDIOCSYNC takes the frame
341number you want to wait for as argument.
342<p>
343It is allowed to call VIDIOCMCAPTURE multiple times (with different
344frame numbers in video_mmap->frame of course) and thus have multiple
345outstanding capture requests. A simple way do to double-buffering
346using this feature looks like this:
347<pre>
348/* setup everything */
349VIDIOCMCAPTURE(0)
350while (whatever) {
351 VIDIOCMCAPTURE(1)
352 VIDIOCSYNC(0)
353 /* process frame 0 while the hardware captures frame 1 */
354 VIDIOCMCAPTURE(0)
355 VIDIOCSYNC(1)
356 /* process frame 1 while the hardware captures frame 0 */
357}
358</pre>
359Note that you are <em>not</em> limited to only two frames. The API
360allows up to 32 frames, the VIDIOCGMBUF ioctl returns the number of
361frames the driver granted. Thus it is possible to build deeper queues
362to avoid loosing frames on load peaks.
363<p>
364While capturing to memory the driver will make a "best effort" attempt
365to capture to screen as well if requested. This normally means all
366frames that "miss" memory mapped capture will go to the display.
367<P>
368A final ioctl exists to allow a device to obtain related devices if a
369driver has multiple components (for example video0 may not be associated
370with vbi0 which would cause an intercast display program to make a bad
371mistake). The VIDIOCGUNIT ioctl reports the unit numbers of the associated
372devices if any exist. The video_unit structure has the following fields.
373<P>
374<TABLE>
375<TR><TD><b>video</b><TD>Video capture device</TD>
376<TR><TD><b>vbi</b><TD>VBI capture device</TD>
377<TR><TD><b>radio</b><TD>Radio device</TD>
378<TR><TD><b>audio</b><TD>Audio mixer</TD>
379<TR><TD><b>teletext</b><TD>Teletext device</TD>
380</TABLE>
381<P>
382<H3>RDS Datastreams</H3>
383For radio devices that support it, it is possible to receive Radio Data
384System (RDS) data by means of a read() on the device. The data is packed in
385groups of three, as follows:
386<TABLE>
387<TR><TD>First Octet</TD><TD>Least Significant Byte of RDS Block</TD></TR>
388<TR><TD>Second Octet</TD><TD>Most Significant Byte of RDS Block
389<TR><TD>Third Octet</TD><TD>Bit 7:</TD><TD>Error bit. Indicates that
390an uncorrectable error occurred during reception of this block.</TD></TR>
391<TR><TD>&nbsp;</TD><TD>Bit 6:</TD><TD>Corrected bit. Indicates that
392an error was corrected for this data block.</TD></TR>
393<TR><TD>&nbsp;</TD><TD>Bits 5-3:</TD><TD>Received Offset. Indicates the
394offset received by the sync system.</TD></TR>
395<TR><TD>&nbsp;</TD><TD>Bits 2-0:</TD><TD>Offset Name. Indicates the
396offset applied to this data.</TD></TR>
397</TABLE>
398</BODY>
399</HTML>
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