v4l2 command
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v4l2 - Video For Linux Two interface


package require v4l2
v4l2 option ?arg ...?


This command provides several operations to interface Video For Linux Two in order to operate camera devices. option indicates what to carry out on the Video For Linux Two subsystem. Any unique abbreviation for option is acceptable. The valid options are:

v4l2 close devid

Closes the device identified by devid which has been opened before using v4l2 open.

v4l2 counters devid

Reports a two element list of statistic counters on the device identified by devid. The first element is the number of video frames received, the second the number of video frames processed with v4l2 image. This information can be used to detect dropped frames.

v4l2 devices

Returns a list of device names which can be used for v4l2 open. If udev 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 /dev directory.

v4l2 image devid ?photoImage?

Copies the most recent captured image of the device devid into the photo image identified by photoImage and returns non-zero on success or zero if no data transfer has taken place. If photoImage 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.

v4l2 info devid

Returns information on open devices. If devid 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 v4l2 open. If devid is omitted, a list of devids, i.e. all currently opened devices is returned.

v4l2 listen ?callback?

Retrieves or sets the callback 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 (add or remove) and the device name which was added or removed. Only useable if udev support is available.

v4l2 mirror devid ?x y?

Retrieves or sets flags to mirror captured images along the X or Y axis. Parameters x and y if specified must be boolean values.

v4l2 open devname callback

Opens the device with device name (UN*X pathname) devname and establishes callback as command to be invoked on captured images and returns a devid, i.e. a handle to further deal with the device. Two additional parameters are appended when callback is invoked: the first is the devid 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 error is used instead of the frame counter.

v4l2 orientation devid ?degrees?

Retrieves or sets the orientation of captured images regarding image rotation. degrees if specified must be an integer number.

v4l2 parameters devid ?key value ...?

Returns or changes device parameters for the device identified by devid given as key-value pairs, e.g. frame-size 320x240 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 array set or dict get.

v4l2 start devid

Starts capturing images of the device identified by devid. When an image is ready, the callback command set on v4l2 open is invoked.

v4l2 state devid

Returns the image capture state of the device identified by devid. The result is the string capture if the device is started, stopped if the device is stopped, or error if an error has been detected while image capture was active.

v4l2 stop devid

Stop capturing images of the device identified by devid.