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author | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
commit | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch) | |
tree | 0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/video4linux/API.html | |
download | lwn-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz lwn-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.zip |
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Diffstat (limited to 'Documentation/video4linux/API.html')
-rw-r--r-- | Documentation/video4linux/API.html | 399 |
1 files changed, 399 insertions, 0 deletions
diff --git a/Documentation/video4linux/API.html b/Documentation/video4linux/API.html new file mode 100644 index 000000000000..4b3d8f640a4a --- /dev/null +++ b/Documentation/video4linux/API.html @@ -0,0 +1,399 @@ +<HTML><HEAD> +<TITLE>Video4Linux Kernel API Reference v0.1:19990430</TITLE> +</HEAD> +<! Revision History: > +<! 4/30/1999 - Fred Gleason (fredg@wava.com)> +<! Documented extensions for the Radio Data System (RDS) extensions > +<BODY bgcolor="#ffffff"> +<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> </TD><TD>Bit 6:</TD><TD>Corrected bit. Indicates that +an error was corrected for this data block.</TD></TR> +<TR><TD> </TD><TD>Bits 5-3:</TD><TD>Received Offset. Indicates the +offset received by the sync system.</TD></TR> +<TR><TD> </TD><TD>Bits 2-0:</TD><TD>Offset Name. Indicates the +offset applied to this data.</TD></TR> +</TABLE> +</BODY> +</HTML> |