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<TITLE>Video4Linux Kernel API Reference v0.1:19990430</TITLE>
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<! Revision History: >
<!   4/30/1999 - Fred Gleason (fredg@wava.com)>
<! Documented extensions for the Radio Data System (RDS) extensions >
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<H3>Devices</H3>
Video4Linux provides the following sets of device files. These live on the
character device formerly known as "/dev/bttv". /dev/bttv should be a
symlink to /dev/video0 for most people. 
<P>
<TABLE>
<TR><TH>Device Name</TH><TH>Minor Range</TH><TH>Function</TH>
<TR><TD>/dev/video</TD><TD>0-63</TD><TD>Video Capture Interface</TD>
<TR><TD>/dev/radio</TD><TD>64-127</TD><TD>AM/FM Radio Devices</TD>
<TR><TD>/dev/vtx</TD><TD>192-223</TD><TD>Teletext Interface Chips</TD>
<TR><TD>/dev/vbi</TD><TD>224-239</TD><TD>Raw VBI Data (Intercast/teletext)</TD>
</TABLE>
<P>
Video4Linux programs open and scan the devices to find what they are looking
for. Capability queries define what each interface supports. The 
described API is only defined for video capture cards. The relevant subset
applies to radio cards. Teletext interfaces talk the existing VTX API.
<P>
<H3>Capability Query Ioctl</H3>
The <B>VIDIOCGCAP</B> ioctl call is used to obtain the capability
information for a video device. The <b>struct video_capability</b> object
passed to the ioctl is completed and returned. It contains the following
information
<P>
<TABLE>
<TR><TD><b>name[32]</b><TD>Canonical name for this interface</TD>
<TR><TD><b>type</b><TD>Type of interface</TD>
<TR><TD><b>channels</b><TD>Number of radio/tv channels if appropriate</TD>
<TR><TD><b>audios</b><TD>Number of audio devices if appropriate</TD>
<TR><TD><b>maxwidth</b><TD>Maximum capture width in pixels</TD>
<TR><TD><b>maxheight</b><TD>Maximum capture height in pixels</TD>
<TR><TD><b>minwidth</b><TD>Minimum capture width in pixels</TD>
<TR><TD><b>minheight</b><TD>Minimum capture height in pixels</TD>
</TABLE>
<P>
The type field lists the capability flags for the device. These are
as follows
<P>
<TABLE>
<TR><TH>Name</TH><TH>Description</TH>
<TR><TD><b>VID_TYPE_CAPTURE</b><TD>Can capture to memory</TD>
<TR><TD><b>VID_TYPE_TUNER</b><TD>Has a tuner of some form</TD>
<TR><TD><b>VID_TYPE_TELETEXT</b><TD>Has teletext capability</TD>
<TR><TD><b>VID_TYPE_OVERLAY</b><TD>Can overlay its image onto the frame buffer</TD>
<TR><TD><b>VID_TYPE_CHROMAKEY</b><TD>Overlay is Chromakeyed</TD>
<TR><TD><b>VID_TYPE_CLIPPING</b><TD>Overlay clipping is supported</TD>
<TR><TD><b>VID_TYPE_FRAMERAM</b><TD>Overlay overwrites frame buffer memory</TD>
<TR><TD><b>VID_TYPE_SCALES</b><TD>The hardware supports image scaling</TD>
<TR><TD><b>VID_TYPE_MONOCHROME</b><TD>Image capture is grey scale only</TD>
<TR><TD><b>VID_TYPE_SUBCAPTURE</b><TD>Capture can be of only part of the image</TD>
</TABLE>
<P>
The minimum and maximum sizes listed for a capture device do not imply all
that all height/width ratios or sizes within the range are possible. A
request to set a size will be honoured by the largest available capture
size whose capture is no large than the requested rectangle in either
direction. For example the quickcam has 3 fixed settings. 
<P>
<H3>Frame Buffer</H3>
Capture cards that drop data directly onto the frame buffer must be told the
base address of the frame buffer, its size and organisation. This is a 
privileged ioctl and one that eventually X itself should set.
<P>
The <b>VIDIOCSFBUF</b> ioctl sets the frame buffer parameters for a capture
card. If the card does not do direct writes to the frame buffer then this
ioctl will be unsupported. The <b>VIDIOCGFBUF</b> ioctl returns the
currently used parameters. The structure used in both cases is a 
<b>struct video_buffer</b>.
<P>
<TABLE>
<TR><TD><b>void *base</b></TD><TD>Base physical address of the buffer</TD>
<TR><TD><b>int height</b></TD><TD>Height of the frame buffer</TD>
<TR><TD><b>int width</b></TD><TD>Width of the frame buffer</TD>
<TR><TD><b>int depth</b></TD><TD>Depth of the frame buffer</TD>
<TR><TD><b>int bytesperline</b></TD><TD>Number of bytes of memory between the start of two adjacent lines</TD>
</TABLE>
<P>
Note that these values reflect the physical layout of the frame buffer. 
The visible area may be smaller. In fact under XFree86 this is commonly the
case. XFree86 DGA can provide the parameters required to set up this ioctl.
Setting the base address to NULL indicates there is no physical frame buffer
access.
<P>
<H3>Capture Windows</H3>
The capture area is described by a <b>struct video_window</b>. This defines
a capture area and the clipping information if relevant. The 
<b>VIDIOCGWIN</b> ioctl recovers the current settings and the 
<b>VIDIOCSWIN</b> sets new values. A successful call to <b>VIDIOCSWIN</b> 
indicates that a suitable set of parameters have been chosen. They do not
indicate that exactly what was requested was granted. The program should
call <b>VIDIOCGWIN</b> to check if the nearest match was suitable. The
<b>struct video_window</b> contains the following fields.
<P>
<TABLE>
<TR><TD><b>x</b><TD>The X co-ordinate specified in X windows format.</TD>
<TR><TD><b>y</b><TD>The Y co-ordinate specified in X windows format.</TD>
<TR><TD><b>width</b><TD>The width of the image capture.</TD>
<TR><TD><b>height</b><TD>The height of the image capture.</TD>
<TR><TD><b>chromakey</b><TD>A host order RGB32 value for the chroma key.</TD>
<TR><TD><b>flags</b><TD>Additional capture flags.</TD>
<TR><TD><b>clips</b><TD>A list of clipping rectangles. <em>(Set only)</em></TD>
<TR><TD><b>clipcount</b><TD>The number of clipping rectangles. <em>(Set only)</em></TD>
</TABLE>
<P>
Clipping rectangles are passed as an array. Each clip consists of the following
fields available to the user.
<P>
<TABLE>
<TR><TD><b>x</b></TD><TD>X co-ordinate of rectangle to skip</TD>
<TR><TD><b>y</b></TD><TD>Y co-ordinate of rectangle to skip</TD>
<TR><TD><b>width</b></TD><TD>Width of rectangle to skip</TD>
<TR><TD><b>height</b></TD><TD>Height of rectangle to skip</TD>
</TABLE>
<P>
Merely setting the window does not enable capturing. Overlay capturing
(i.e. PCI-PCI transfer to the frame buffer of the video card)
is activated by passing the <b>VIDIOCCAPTURE</b> ioctl a value of 1, and
disabled by passing it a value of 0. 
<P>
Some capture devices can capture a subfield of the image they actually see.
This is indicated when VIDEO_TYPE_SUBCAPTURE is defined.
The video_capture describes the time and special subfields to capture.
The video_capture structure contains the following fields.
<P>
<TABLE>
<TR><TD><b>x</b></TD><TD>X co-ordinate of source rectangle to grab</TD>
<TR><TD><b>y</b></TD><TD>Y co-ordinate of source rectangle to grab</TD>
<TR><TD><b>width</b></TD><TD>Width of source rectangle to grab</TD>
<TR><TD><b>height</b></TD><TD>Height of source rectangle to grab</TD>
<TR><TD><b>decimation</b></TD><TD>Decimation to apply</TD>
<TR><TD><b>flags</b></TD><TD>Flag settings for grabbing</TD>
</TABLE>
The available flags are
<P>
<TABLE>
<TR><TH>Name</TH><TH>Description</TH>
<TR><TD><b>VIDEO_CAPTURE_ODD</b><TD>Capture only odd frames</TD>
<TR><TD><b>VIDEO_CAPTURE_EVEN</b><TD>Capture only even frames</TD>
</TABLE>
<P>
<H3>Video Sources</H3>
Each video4linux video or audio device captures from one or more 
source <b>channels</b>. Each channel can be queries with the 
<b>VDIOCGCHAN</b> ioctl call. Before invoking this function the caller
must set the channel field to the channel that is being queried. On return
the <b>struct video_channel</b> is filled in with information about the
nature of the channel itself.
<P>
The <b>VIDIOCSCHAN</b> ioctl takes an integer argument and switches the
capture to this input. It is not defined whether parameters such as colour
settings or tuning are maintained across a channel switch. The caller should
maintain settings as desired for each channel. (This is reasonable as 
different video inputs may have different properties).
<P>
The <b>struct video_channel</b> consists of the following
<P>
<TABLE>
<TR><TD><b>channel</b></TD><TD>The channel number</TD>
<TR><TD><b>name</b></TD><TD>The input name - preferably reflecting the label
on the card input itself</TD>
<TR><TD><b>tuners</b></TD><TD>Number of tuners for this input</TD>
<TR><TD><b>flags</b></TD><TD>Properties the tuner has</TD>
<TR><TD><b>type</b></TD><TD>Input type (if known)</TD>
<TR><TD><b>norm</b><TD>The norm for this channel</TD>
</TABLE>
<P>
The flags defined are
<P>
<TABLE>
<TR><TD><b>VIDEO_VC_TUNER</b><TD>Channel has tuners.</TD>
<TR><TD><b>VIDEO_VC_AUDIO</b><TD>Channel has audio.</TD>
<TR><TD><b>VIDEO_VC_NORM</b><TD>Channel has norm setting.</TD>
</TABLE>
<P>
The types defined are
<P>
<TABLE>
<TR><TD><b>VIDEO_TYPE_TV</b><TD>The input is a TV input.</TD>
<TR><TD><b>VIDEO_TYPE_CAMERA</b><TD>The input is a camera.</TD>
</TABLE>
<P>
<H3>Image Properties</H3>
The image properties of the picture can be queried with the <b>VIDIOCGPICT</b>
ioctl which fills in a <b>struct video_picture</b>. The <b>VIDIOCSPICT</b> 
ioctl allows values to be changed. All values except for the palette type
are scaled between 0-65535. 
<P>
The <b>struct video_picture</b> consists of the following fields
<P>
<TABLE>
<TR><TD><b>brightness</b><TD>Picture brightness</TD>
<TR><TD><b>hue</b><TD>Picture hue (colour only)</TD>
<TR><TD><b>colour</b><TD>Picture colour (colour only)</TD>
<TR><TD><b>contrast</b><TD>Picture contrast</TD>
<TR><TD><b>whiteness</b><TD>The whiteness (greyscale only)</TD>
<TR><TD><b>depth</b><TD>The capture depth (may need to match the frame buffer depth)</TD>
<TR><TD><b>palette</b><TD>Reports the palette that should be used for this image</TD>
</TABLE>
<P>
The following palettes are defined
<P>
<TABLE>
<TR><TD><b>VIDEO_PALETTE_GREY</b><TD>Linear intensity grey scale (255 is brightest).</TD>
<TR><TD><b>VIDEO_PALETTE_HI240</b><TD>The BT848 8bit colour cube.</TD>
<TR><TD><b>VIDEO_PALETTE_RGB565</b><TD>RGB565 packed into 16 bit words.</TD>
<TR><TD><b>VIDEO_PALETTE_RGB555</b><TD>RGV555 packed into 16 bit words, top bit undefined.</TD>
<TR><TD><b>VIDEO_PALETTE_RGB24</b><TD>RGB888 packed into 24bit words.</TD>
<TR><TD><b>VIDEO_PALETTE_RGB32</b><TD>RGB888 packed into the low 3 bytes of 32bit words. The top 8bits are undefined.</TD>
<TR><TD><b>VIDEO_PALETTE_YUV422</b><TD>Video style YUV422 - 8bits packed 4bits Y 2bits U 2bits V</TD>
<TR><TD><b>VIDEO_PALETTE_YUYV</b><TD>Describe me</TD>
<TR><TD><b>VIDEO_PALETTE_UYVY</b><TD>Describe me</TD>
<TR><TD><b>VIDEO_PALETTE_YUV420</b><TD>YUV420 capture</TD>
<TR><TD><b>VIDEO_PALETTE_YUV411</b><TD>YUV411 capture</TD>
<TR><TD><b>VIDEO_PALETTE_RAW</b><TD>RAW capture (BT848)</TD>
<TR><TD><b>VIDEO_PALETTE_YUV422P</b><TD>YUV 4:2:2 Planar</TD>
<TR><TD><b>VIDEO_PALETTE_YUV411P</b><TD>YUV 4:1:1 Planar</TD>
</TABLE>
<P>
<H3>Tuning</H3>
Each video input channel can have one or more tuners associated with it. Many
devices will not have tuners. TV cards and radio cards will have one or more
tuners attached.
<P>
Tuners are described by a <b>struct video_tuner</b> which can be obtained by
the <b>VIDIOCGTUNER</b> ioctl. Fill in the tuner number in the structure
then pass the structure to the ioctl to have the data filled in. The 
tuner can be switched using <b>VIDIOCSTUNER</b> which takes an integer argument
giving the tuner to use. A struct tuner has the following fields
<P>
<TABLE>
<TR><TD><b>tuner</b><TD>Number of the tuner</TD>
<TR><TD><b>name</b><TD>Canonical name for this tuner (eg FM/AM/TV)</TD>
<TR><TD><b>rangelow</b><TD>Lowest tunable frequency</TD>
<TR><TD><b>rangehigh</b><TD>Highest tunable frequency</TD>
<TR><TD><b>flags</b><TD>Flags describing the tuner</TD>
<TR><TD><b>mode</b><TD>The video signal mode if relevant</TD>
<TR><TD><b>signal</b><TD>Signal strength if known - between 0-65535</TD>
</TABLE>
<P>
The following flags exist
<P>
<TABLE>
<TR><TD><b>VIDEO_TUNER_PAL</b><TD>PAL tuning is supported</TD>
<TR><TD><b>VIDEO_TUNER_NTSC</b><TD>NTSC tuning is supported</TD>
<TR><TD><b>VIDEO_TUNER_SECAM</b><TD>SECAM tuning is supported</TD>
<TR><TD><b>VIDEO_TUNER_LOW</b><TD>Frequency is in a lower range</TD>
<TR><TD><b>VIDEO_TUNER_NORM</b><TD>The norm for this tuner is settable</TD>
<TR><TD><b>VIDEO_TUNER_STEREO_ON</b><TD>The tuner is seeing stereo audio</TD>
<TR><TD><b>VIDEO_TUNER_RDS_ON</b><TD>The tuner is seeing a RDS datastream</TD>
<TR><TD><b>VIDEO_TUNER_MBS_ON</b><TD>The tuner is seeing a MBS datastream</TD>
</TABLE>
<P>
The following modes are defined
<P>
<TABLE>
<TR><TD><b>VIDEO_MODE_PAL</b><TD>The tuner is in PAL mode</TD>
<TR><TD><b>VIDEO_MODE_NTSC</b><TD>The tuner is in NTSC mode</TD>
<TR><TD><b>VIDEO_MODE_SECAM</b><TD>The tuner is in SECAM mode</TD>
<TR><TD><b>VIDEO_MODE_AUTO</b><TD>The tuner auto switches, or mode does not apply</TD>
</TABLE>
<P>
Tuning frequencies are an unsigned 32bit value in 1/16th MHz or if the
<b>VIDEO_TUNER_LOW</b> flag is set they are in 1/16th KHz. The current
frequency is obtained as an unsigned long via the <b>VIDIOCGFREQ</b> ioctl and
set by the <b>VIDIOCSFREQ</b> ioctl.
<P>
<H3>Audio</H3>
TV and Radio devices have one or more audio inputs that may be selected. 
The audio properties are queried by passing a <b>struct video_audio</b> to <b>VIDIOCGAUDIO</b> ioctl. The
<b>VIDIOCSAUDIO</b> ioctl sets audio properties.
<P>
The structure contains the following fields
<P>
<TABLE>
<TR><TD><b>audio</b><TD>The channel number</TD>
<TR><TD><b>volume</b><TD>The volume level</TD>
<TR><TD><b>bass</b><TD>The bass level</TD>
<TR><TD><b>treble</b><TD>The treble level</TD>
<TR><TD><b>flags</b><TD>Flags describing the audio channel</TD>
<TR><TD><b>name</b><TD>Canonical name for the audio input</TD>
<TR><TD><b>mode</b><TD>The mode the audio input is in</TD>
<TR><TD><b>balance</b><TD>The left/right balance</TD>
<TR><TD><b>step</b><TD>Actual step used by the hardware</TD>
</TABLE>
<P>
The following flags are defined
<P>
<TABLE>
<TR><TD><b>VIDEO_AUDIO_MUTE</b><TD>The audio is muted</TD>
<TR><TD><b>VIDEO_AUDIO_MUTABLE</b><TD>Audio muting is supported</TD>
<TR><TD><b>VIDEO_AUDIO_VOLUME</b><TD>The volume is controllable</TD>
<TR><TD><b>VIDEO_AUDIO_BASS</b><TD>The bass is controllable</TD>
<TR><TD><b>VIDEO_AUDIO_TREBLE</b><TD>The treble is controllable</TD>
<TR><TD><b>VIDEO_AUDIO_BALANCE</b><TD>The balance is controllable</TD>
</TABLE>
<P>
The following decoding modes are defined
<P>
<TABLE>
<TR><TD><b>VIDEO_SOUND_MONO</b><TD>Mono signal</TD>
<TR><TD><b>VIDEO_SOUND_STEREO</b><TD>Stereo signal (NICAM for TV)</TD>
<TR><TD><b>VIDEO_SOUND_LANG1</b><TD>European TV alternate language 1</TD>
<TR><TD><b>VIDEO_SOUND_LANG2</b><TD>European TV alternate language 2</TD>
</TABLE>
<P>
<H3>Reading Images</H3>
Each call to the <b>read</b> syscall returns the next available image
from the device. It is up to the caller to set format and size (using
the VIDIOCSPICT and VIDIOCSWIN ioctls) and then to pass a suitable
size buffer and length to the function. Not all devices will support
read operations.
<P>
A second way to handle image capture is via the mmap interface if supported.
To use the mmap interface a user first sets the desired image size and depth
properties. Next the VIDIOCGMBUF ioctl is issued. This reports the size
of buffer to mmap and the offset within the buffer for each frame. The
number of frames supported is device dependent and may only be one. 
<P>
The video_mbuf structure contains the following fields
<P>
<TABLE>
<TR><TD><b>size</b><TD>The number of bytes to map</TD>
<TR><TD><b>frames</b><TD>The number of frames</TD>
<TR><TD><b>offsets</b><TD>The offset of each frame</TD>
</TABLE>
<P>
Once the mmap has been made the VIDIOCMCAPTURE ioctl starts the
capture to a frame using the format and image size specified in the
video_mmap (which should match or be below the initial query size).
When the VIDIOCMCAPTURE ioctl returns the frame is <em>not</em>
captured yet, the driver just instructed the hardware to start the
capture.  The application has to use the VIDIOCSYNC ioctl to wait
until the capture of a frame is finished.  VIDIOCSYNC takes the frame
number you want to wait for as argument.
<p>
It is allowed to call VIDIOCMCAPTURE multiple times (with different
frame numbers in video_mmap->frame of course) and thus have multiple
outstanding capture requests.  A simple way do to double-buffering
using this feature looks like this:
<pre>
/* setup everything */
VIDIOCMCAPTURE(0)
while (whatever) {
   VIDIOCMCAPTURE(1)
   VIDIOCSYNC(0)
   /* process frame 0 while the hardware captures frame 1 */
   VIDIOCMCAPTURE(0)
   VIDIOCSYNC(1)
   /* process frame 1 while the hardware captures frame 0 */
}
</pre>
Note that you are <em>not</em> limited to only two frames.  The API
allows up to 32 frames, the VIDIOCGMBUF ioctl returns the number of
frames the driver granted.  Thus it is possible to build deeper queues
to avoid loosing frames on load peaks.
<p>
While capturing to memory the driver will make a "best effort" attempt
to capture to screen as well if requested. This normally means all
frames that "miss" memory mapped capture will go to the display.
<P>
A final ioctl exists to allow a device to obtain related devices if a
driver has multiple components (for example video0 may not be associated
with vbi0 which would cause an intercast display program to make a bad
mistake). The VIDIOCGUNIT ioctl reports the unit numbers of the associated
devices if any exist. The video_unit structure has the following fields.
<P>
<TABLE>
<TR><TD><b>video</b><TD>Video capture device</TD>
<TR><TD><b>vbi</b><TD>VBI capture device</TD>
<TR><TD><b>radio</b><TD>Radio device</TD>
<TR><TD><b>audio</b><TD>Audio mixer</TD>
<TR><TD><b>teletext</b><TD>Teletext device</TD>
</TABLE>
<P>
<H3>RDS Datastreams</H3>
For radio devices that support it, it is possible to receive Radio Data
System (RDS) data by means of a read() on the device.  The data is packed in
groups of three, as follows:
<TABLE>
<TR><TD>First Octet</TD><TD>Least Significant Byte of RDS Block</TD></TR>
<TR><TD>Second Octet</TD><TD>Most Significant Byte of RDS Block
<TR><TD>Third Octet</TD><TD>Bit 7:</TD><TD>Error bit.  Indicates that
an uncorrectable error occurred during reception of this block.</TD></TR>
<TR><TD>&nbsp;</TD><TD>Bit 6:</TD><TD>Corrected bit.  Indicates that  
an error was corrected for this data block.</TD></TR>
<TR><TD>&nbsp;</TD><TD>Bits 5-3:</TD><TD>Received Offset.  Indicates the  
offset received by the sync system.</TD></TR>
<TR><TD>&nbsp;</TD><TD>Bits 2-0:</TD><TD>Offset Name.  Indicates the  
offset applied to this data.</TD></TR>
</TABLE>
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