D 2016-07-07T08:51:19.587
L v4l2\scommand
P e1fbf5651da2c4e3192d7c229f5828bd7802dd10
U chw
W 4900
<h2>Name</h2>
<b>v4l2</b> - Video For Linux Two interface
<h2>Synopsis</h2>
<tt>package require v4l2</tt><br>
<tt>v4l2 <i>option</i> ?<i>arg ...</i>?</tt>
<h2>Description</h2>
This command provides several operations to interface Video For Linux
Two in order to operate camera devices. <tt><i>option</i></tt> indicates what
to carry out on the Video For Linux Two subsystem. Any unique
abbreviation for <tt><i>option</i></tt> is acceptable.
The valid options are:
<tt>v4l2 close <i>devid</i></tt>
Closes the device identified by <tt><i>devid</i></tt> which has been opened before using <tt>v4l2 open</tt>.
<tt>v4l2 counters <i>devid</i></tt>
Reports a two element list of statistic counters on the device identified by <tt><i>devid</i></tt>. The first element is the number of video frames received, the second the number of video frames processed with <tt>v4l2 image</tt>. This information can be used to detect dropped frames.
<tt>v4l2 devices</tt>
Returns a list of device names which can be used for <tt>v4l2 open</tt>. If <tt>udev</tt> support is available, this list is refreshed on plug and unplug of devices. Otherwise it is made up of a snapshot of suitable file names in the <tt>/dev</tt> directory.
<tt>v4l2 image <i>devid</i> ?<i>photoImage</i>?</tt>
Copies the most recent captured image of the device <tt><i>devid</i></tt> into the photo image identified by <tt><i>photoImage</i></tt> and returns non-zero on success or zero if no data transfer has taken place. If <tt><i>photoImage</i></tt> is omitted, a four element list is returned with the first element being the image width, the second the image height, the third the number of bytes per pixel, and the last the image's RGB values with 3 bytes per pixel in red, green, blue order as a byte array. In this case an error is indicated by throwing an exception.
<tt>v4l2 info <i>devid</i></tt>
Returns information on open devices. If <tt><i>devid</i></tt> is specified,
a list of two elements is returned, the first being the device name and
the second the image callback command for that device, i.e. the same
arguments which were used on <tt>v4l2 open</tt>. If <tt><i>devid</i></tt> is omitted, a list of <tt><i>devid</i></tt>s, i.e. all currently opened devices is returned.
<tt>v4l2 listen ?<i>callback</i>?</tt>
Retrieves or sets the <tt><i>callback</i></tt> command called on plug and unplug of devices. When a device is plugged or unplugged that callback is invoked with two additional arguments: the type of event (<tt>add</tt> or <tt>remove</tt>) and the device name which was added or removed. Only useable if <tt>udev</tt> support is available.
<tt>v4l2 mirror <i>devid</i> ?<i>x y</i>?</tt>
Retrieves or sets flags to mirror captured images along the X or Y axis. Parameters <tt><i>x</i></tt> and <tt><i>y</i></tt> if specified must be boolean values.
<tt>v4l2 open <i>devname callback</i></tt>
Opens the device with device name (UN*X pathname) <tt><i>devname</i></tt> and establishes <tt><i>callback</i></tt> as command to be invoked on captured images and returns a <tt><i>devid</i></tt>, i.e. a handle to further deal with the device. Two additional parameters are appended when <tt><i>callback</i></tt> is invoked: the first is the <tt><i>devid</i></tt> of the device, the second a frame counter with initial value of zero based on the last start of image capture. If an error is detected during image capture, the word <tt>error</tt> is used instead of the frame counter.
<tt>v4l2 orientation <i>devid</i> ?<i>degrees</i>?</tt>
Retrieves or sets the orientation of captured images regarding image rotation. <tt><i>degrees</i></tt> if specified must be an integer number.
<tt>v4l2 parameters <i>devid</i> ?<i>key value ...</i>?</tt>
Returns or changes device parameters for the device identified by <tt><i>devid</i></tt> given as key-value pairs, e.g. <tt>frame-size 320x240</tt> will change the size of captured images to width 320 and height 240. The command returns the current device parameters (after the potential change, when keys and values where given) as a key-value list which can be processed with <tt>array set</tt> or <tt>dict get</tt>.
<tt>v4l2 start <i>devid</i></tt>
Starts capturing images of the device identified by <tt><i>devid</i></tt>. When an image is ready, the callback command set on <tt>v4l2 open</tt> is invoked.
<tt>v4l2 state <i>devid</i></tt>
Returns the image capture state of the device identified by <tt><i>devid</i></tt>. The result is the string <tt>capture</tt> if the device is started, <tt>stopped</tt> if the device is stopped, or <tt>error</tt> if an error has been detected while image capture was active.
<tt>v4l2 stop <i>devid</i></tt>
Stop capturing images of the device identified by <tt><i>devid</i></tt>.
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