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Hack 64. Motion Capture and Video Conferencing Fun

Keep an eye on the world with your
webcam.

Some years back, it was the height of geek cred to have a
webcam. At that point in history, the average webcam was a hulking
device that looked more like a CCTV camera and cost an inordinate
amount of money. Many of these bulky units also needed an expensive
video card to squeeze the huge amounts of data through weedy
`486 processors. Since those early days, the success
of the webcam has catapulted and virtually everyone has picked one up
for peanuts.

With this explosion of webcams and the rapid growth in broadband
speed, videoconferencing has become something of a reality. [Hack #63] covered how to use the
GnomeMeeting application to make phone calls over the Internet. In
this hack, I cover the video conferencing side of GnomeMeeting as
well as explore how to enable motion capture so that you can use it
to form a security system in your home/office.

8.11.1. Setting Up a Webcam

Before you get started using GnomeMeeting
and motion capture, the first step is to ensure that you have a
working webcam configured. With more and more people using Project
Utopia [Hack #93], device
configuration is becoming less of an issue, but it probably needs a
brief discussion.

First, you should find out which driver your webcam needs. A number
of online hardware databases and some sensible Google searching can
help you with this. Then you can find out if that driver is included
in your kernel version or if you need to upgrade to a later kernel
[Hack #89] that does support your
webcam. If the driver is not included in the latest kernel version or
you need a newer version of the driver than the one
that's included in the kernel tree, you will
probably need to patch the kernel source to get the driver you need.

In addition to using a driver for your webcam, you should also ensure
that you compile Video 4 Linux support into your kernel. Video 4
Linux provides a standardized method for the kernel to handle video
devices. Support for this is in the main kernel tree. It is
recommended that this be compiled as a module that can be loaded when
you access your webcam.

Most webcams are USB-powered, so you need to ensure that your USB
system is configured correctly [Hack #93] . When you plug in a camera,
it should load the Video 4 Linux module. Check that it does with this
command:

foo@Bar:~$ lsmod

In the output you should see videodev listed. If
it is not listed, you should insert it with
insmod:

foo@bar:~$ insmod videodev

Once Video 4 Linux is loaded, it creates one or more
video entries in /dev.
Check this with:

foo@bar:~$ ls -al /dev/video*

When you run this command, you should see at least one entry appear.
If this is not the case, your camera is not working with Linux. You
should double-check your previous work to make sure you did
everything necessary.

8.11.2. Using GnomeMeeting

When you first run GnomeMeeting,
you
are taken through a configuration druid that helps you set up and
configure the program. Included in this setup routine are some
features for ensuring your webcam is working properly. At the end of
this process, you can click the webcam icon and see the video from
your camera in the window.

If you see a corrupted picture when viewing video in GnomeMeeting,
the webcam driver might have some bugs that might require an update
to a newer driver version; this has been a problem with the OV511
chip-based range of devices. You should check your camera with a
range of software such as xawtv or Camorama. If
you can get video working in other tools, it might be a problem with
how GnomeMeeting is accessing the device. If this is the case, you
should contact the GnomeMeeting developers at http://www.gnomemeeting.org.

8.11.3. Creating a Motion Capture Camera

The concept of motion capture is fairly simple. You set up a camera in
a particular location and the camera registers when a particular
threshold of pixels changes. As an example, you could have a camera
focused on a room, and if someone walks past the camera the recording
software is triggered by the motion.

This hack covers a tool called motion that is
incredibly flexible in dealing with a variety of motion capture
needs. What is particularly interesting about
motion is the range of responses that can be
triggered when motion occurs. The software can send you an email,
update a database, save a picture, record a video clip, play a sound,
and more. motion is also flexible in how it is
configured and used.

To get started, first you should install motion
using your distribution package manager, or from the official web
site at http://www.lavrsen.dk/twiki/bin/view/Motion/DownloadFiles.
You also need to download the software dependencies if you want to
save images and movies when movement occurs. Details about these
requirements are on the motion web site.

Running motion is simple; just run it from the
command line:

foo@bar:~$ motion

motion reads a central configuration file called
motion.conf, which is normally stored in
/etc. This easy-to-configure file contains
settings for all features within motion. The
first section that you should concentrate on is called
Capture Device Options. Here you should set
videodevice to the device in
/dev that you are using (this is usually
/dev/video0). You should also adjust the frame
rate, as this affects the accuracy of the webcam. The next important
section to complete is Motion Detection Settings,
where you should set the threshold setting to something that is
suitable. This setting specifies how sensitive the motion capture is.
To test this, run motion, move in front of the
camera, and see how the software reacts. A good test is to look at
the camera, stand still, and move your eyes, mouth, and other parts
of your face to see if the movement triggers the camera.

The rest of the file contains settings that can be used to send you
an email when motion occurs, store information in a database, and
store images and video. If you want to store images and video, you
should ensure that you set the target_dir setting
to a directory where you want to store the images/video.

motion also includes a comprehensive set of
command-line options that negate the need for a configuration file in
some cases. These command-line options are useful if you want to use
motion in a very specific way, possibly in a
script or cronjob. In addition to this flexibility,
motion includes a special
execute option with which you can specify a script
or command that can be executed when motion is detected.