V4L2 Video Capture

Capture video from USB camera using V4L2 framework

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Add-On Required: This feature requires the Embedded Coder Support Package for BeagleBone Black Hardware add-on.

  • V4L2 Video Capture block

Libraries:
Embedded Coder Support Package for BeagleBone Black Hardware

Description

The V4L2 Video Capture block enables you to capture live video from a USB video camera using the Video for Linux Two API (V4L2) driver framework. During simulation, the block outputs a moving colorbar image.

The debian Linux® image on Raspberry Pi® hardware supports video capture from USB cameras compliant with the USB video class (UVC) specification. In addition to being a UVC compliant camera, the camera itself should also support data acquisition in the YUYV mode.

The following cameras have been tested with the V4L2 Video Capture block but is not limited to:

  • Logitech QuickCam Pro 9000

  • Logitech QuickCam Pro 3000

  • Logitech Webcam C600

  • Logitech HD Webcam C310

Sometimes, when you connect a USB webcam to the BeagleBone® Black hardware that was running, the BeagleBone Black hardware does not recognize the USB webcam. To verify that the BeagleBone Black hardware recognizes the USB webcam, in the Command Window, enter:

bbone = beaglebone_black;
system(bbone,'ls -al /dev/videox')

If the board recognizes the USB camera, this command returns the name of the video device associated with the USB camera. Otherwise, restart the BeagleBone Black hardware. After restarting, if the BeagleBone Black hardware does not recognize the USB webcam, is possible that the webcam is not a supported device. Try using a different USB webcam.

Ports

Output

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The block outputs the red component of each pixel.

Dependencies

  • To enable this port, set Pixel format to RGB.

Data Types: uint8

The block outputs the green component of each pixel.

Dependencies

  • To enable this port, set Pixel format to RGB.

Data Types: uint8

The block outputs the blue component of each pixel.

Dependencies

  • To enable this port, set Pixel format to RGB.

Data Types: uint8

The block outputs the luma component of each pixel.

Dependencies

  • To enable this port, set Pixel format to YCbCr 4:2:2.

Data Types: uint8

The block outputs the blue difference component of each pixel.

Dependencies

  • To enable this port, set Pixel format to YCbCr 4:2:2.

Data Types: uint8

The block outputs the red difference component of each pixel.

Dependencies

  • To enable this port, set Pixel format to YCbCr 4:2:2.

Data Types: uint8

Parameters

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Enter the path and name of the video device. The Linux kernel creates a video device file when you connect a supported USB video camera to the target hardware. By default, the Linux kernel supports all UVC devices.

To see the list of video device files, open a command-line session with the board and enter: ls -al /dev/video*.

Select the display resolution of the image in pixels.

Enter the width in pixels and the height in lines of the image.

Dependencies

To enable this parameter, set Image size to custom.

Set the format of the video device to either RGB or YCbCr 4:2:2.

RGB represents the red, green, and blue components of a pixel using an 8-bit value. RGB color space is device-dependent.

YCbCr 4:2:2 uses three channels to represent color image data for each pixel:

  • Y is the luma component (essentially a grayscale signal).

  • Cb is the blue-difference chroma component.

  • Cr is the red-difference chroma component.

The Cb and Cr components are sampled at half the sample rate of Y.

Enter the sample time of the video device. Smaller values require the processor to complete the same number of instructions in less time, which can cause task overruns.

Version History

Introduced in R2014b

See Also

Topics

External Websites