voxl-uvc-server

Overview

voxl-uvc-server is an application which grabs video from UVC cameras and serves up the video as an MPA (Modal Pipe Architecture) pipe for other applications to pull from. This server is often used in conjunction with voxl-streamer.

There are a large array of UVC cameras on the market and we haven’t tested them all, but below is a list of some that we know voxl-uvc-server supports.

In general, voxl-uvc-server supports UVC cameras that have the ability to provide a raw frame output.

Logitech C270
Logitech C930e
Logitech Brio
Videology 5MP Micro USB 2.0 Board Camera
PureThermal Mini with Flir Lepton
Flir Boson 640
Blue Robotics h264 camera

Usage

As with all MPA services, voxl-uvc-server can be configured and enabled to run on boot using it’s configuration script. Usage is as follows:

voxl2:/$ voxl-configure-uvc -h

Start wizard with prompts:
voxl-configure-uvc

Shortcut configuration arguments for scripted setup.
factory_enable will reset the config file to factory defaults
before enabling the service.


voxl-configure-uvc disable
voxl-configure-uvc factory_enable
voxl-configure-uvc enable

show this help message:
voxl-configure-uvc help

Configuring voxl-uvc-server will set up the following default configuration file:

voxl2:/$ cat /etc/modalai/voxl-uvc-server.conf 
/**
 * This file contains configuration that's specific to voxl-uvc-server.
 * parameter descriptions:
 * 
 * width: Desired image width. (e.g. 640)
 * Default is 640.
 *
 * height: Desired image height. (e.g. 480)
 * Default is 480.
 *
 * height: Desired frame rate in fps (e.g. 15).
 * Default is 30.
 *
 * pipe-name: Desired MPA pipe name in /run/mpa (e.g. webcam).
 * Default is uvc.
 *
 */
{
	"pipe_name":	"uvc",
	"width":	640,
	"height":	480,
	"fps":	30
}

If a camera doesn’t support the default configuration, it can be manually tweaked. For example, using the PureThermal Mini with Flir Lepton requires the following configuration options:

{
	"pipe_name":	"uvc",
	"width":	160,
	"height":	120,
	"fps":	9
}

After modifying the configuration file, voxl-uvc-server can be restarted by power cycling or running the following:

systemctl restart voxl-uvc-server

Tips

voxl-uvc-server also provides a few helpful debugging tools in order to troubleshoot issues or determine the required confiuration for a new camera.

The Linux command line utility, lsusb, can be very helpful to see what devices have enumerated on the USB bus. One can run the command with a USB camera attached to see if the camera has enumerated.

voxl2:/$ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 002: ID 046d:0825 Logitech, Inc. Webcam C270
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

One can look at the above output and determine the vendor ID and Product ID of their camera, in this example the vendor ID is 046d, while the product ID is 0825

lsusb -v -d $VENDOR_ID:$PRODUCT_ID can also provide a lot more information about a specific device, for example:

voxl2:/$ lsusb -v -d 046d:0825

Bus 001 Device 002: ID 046d:0825 Logitech, Inc. Webcam C270
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass          239 Miscellaneous Device
  bDeviceSubClass         2
  bDeviceProtocol         1 Interface Association
  bMaxPacketSize0        64
  idVendor           0x046d Logitech, Inc.
  idProduct          0x0825 Webcam C270
  bcdDevice            0.12
  iManufacturer           0
  iProduct                0
  iSerial                 2 9C06CEC0
  bNumConfigurations      1
  ...

voxl-uvc-server also provides a script called show-video-device-info.sh which can be used to get useful information about any attached UVC cameras:

voxl2:/$ show-video-device-info.sh
/dev/video2: UVC Camera (046d:0825) 046d:0825

For debugging purposes, voxl-uvc-server can be ran manually from the command line and has the ability to pass in a few arguments for customization:

voxl2:/$ voxl-uvc-server -h
loading config file
Usage: voxl-uvc-server <options>
Options:
-d                Show extra debug messages
-v <vendor-id>    USB vendor id of the desired UVC device in hexadecimal (e.g. 090c)
                  Default is search for any vendor id
-p <product-id>   USB product id of the desired UVC device in hexadecimal (e.g. 337b)
                  Default is search for any product id
-r <resolution>   Desired image resolution (e.g. 320x240)
                  Default is 640x480
-f <fps>          Desired frame rate in fps (e.g. 15)
                  Default is 30
-l                List all devices found then exit
-o <name>         Custom output name
                  Default is uvc
-h                Show help

These arguments will override the config file at /etc/modalai/voxl-uvc-server.conf

Simultaneous UVC cameras

Due to a bug in libuvc in order to run two USB cameras simultaneously, you need to make one camera have different formatting options than the other. The least intrusive way to do this is to set the frame rate of one camera different than the other.

Here we set the frame rate of the first camera to 25 fps using the -f option:

voxl2:/$ voxl-uvc-server -f 25

Assuming the other camera defaults to 30 fps, you do not need to set it’s frame rate:

voxl2:/$ voxl-uvc-server