7 things to check when
Project lead at Omega Unfold Inc
What happens when a webcam fails to connect?
Connecting webcams on a PC can sometimes fail for many reasons.
When a connection
fails, the following can occur:
- The software may give a connection error for the webcam:
Cable error, driver error, USB overload error
- The software may connect correctly to the webcam, but no images
will stream: Usually an overload error
- If connecting
many cameras, the first cameras will work fine, but the last
camera(s) may fail to connect: Usually a bandwidth error.
A measurement of the
ability of an electronic communications device or system
to send and receive information; especially: a quantity
of information that can be transferred over a connection.
In example: Graphics use more bandwidth than text does.
1. Webcams need more bandwidth than
most USB devices.
Unlike keyboards and mice,
webcams need to stream non-stop big chunks of data. Connecting a
single webcam on a computer is usually not a problem, but the
data transfer amount really starts adding up when connecting a
few webcams. There is a limit to the amount of bandwidth a
connection can support (see point #3 for details)
resolution and framerate matters
a webcam, some software automatically connect to a default
resolution (Zone Trigger software gives this s an option). This
can be ok, but it is preferable to choose a reasonable
resolution for your needs. If you want to take pictures or
record video, you might want to use a high resolution. If you
need to do some motion detection and do not care about beautiful
images, you should choose a lower resolution.
need to compromise between image quality and performance.
If you double the resolution of an image, you actually
multiply by 4 the amount of pixels.
Regarding framerate, doubling the framerate *approximately*
doubles the bandwidth. Why not exactly? Because the most webcams
use compression when transferring data, and compression spreads
across multiple frames.
are many USB controllers on a computer.
USB controllers are chips in the
computer. Each controller has a limit on the amount of data that
it can process (bandwidth limit). And each controller is
connected to one (or many) USB port on the computer.
So if you connect too many
data-hungry devices on the same controller, it will cause an overload,
and some devices will fail to connect properly.
A USB controller will usually not
overload when a single Webcam is being used, or even 2 webcams in
low resolution. It is likely to overload if a software tries to
connect to 3 or more webcams.
connecting the webcams in different USB ports so to spread the
bandwidth over multiple controllers.
Bad news: the ports are not identified as being interfaced with
controller #1 or #2... so you'll have no choice but to
Add some USB controllers.
This is not really an option for most laptops, but desktop
computers are upgradable with cheap USB expansion cards.
Webcam have micropohones
actually contain 2 devices: a video capture and an audio capture
device, and both a considered separate. It is possible to
connect only the video, or only the audio. Some software allow
this choice (Zone Trigger software does).
does not require a lot of bandwidth, it is usually a thin
stream. However, when troubleshooting, it might be an option to
try connecting only the video to see if it will tip the scale.
5. USB2 and
USB3 are not the same
There are many types of USB
interfaces; as technology gets better, better and faster
interfaces hit the market. USB 3 is much faster than USB 2. Many
computers have 2 different types of interfaces. You can tell the
difference between USB 2 and USB3 by the connection's color. As
a general rule, USB2 is black and USB3 is blue.
Why have both types on one computer?
Because some devices work better on their native interface.
Usually, we can swap connections without an issue, but every now
and then a device will snob the connection. Some USB3 devices
will ONLY work on USB3 (ie: Microsoft Kinect V2). There
also is a cost to backward compatibility; connecting a USB2
device on a USB3 port can add some overhead to the bandwidth.
webcam's software driver matters
Different webcams set at the same
resolution and framerate can require different amount of bandwidth.
The webcam's driver plays a role in this: communication between
webcam and the driver is usually compressed, some manufacturers
compress the stream more than others.
A compressed stream is a good thing for transmission
speed and bandwidth, but can lead to a lower quality image. This
compromise manufacturers need to make.
Obviously, if the
stream if more compressed, it will be possible to have more
webcams on the same USB controller. Sadly, this is not really
something that the user has any control over.
USB cable and hubs may fail beyond 10 feet
USB cable will
often loose its signal if too long extension is used, which is actually not
so long. USB devices usually don't have a cable length above 6
feet, and a 6 feet extension is *usually* stable,
but anything longer is playing with fire. Any source of
magnetism in proximity can reduce the reliability of
In order to have a reliable connection when using
extensions, you should use an amplified extension, also called
Active USB cable. The cable looks like a normal cable,
but it uses power from the USB cable to amplify the USB signal.
Same goes for USB hubs. In theory, each
USB connection on the PC could support up to 128 devices
chained on hubs (hubs count as devices). In practice, not so
much. Each device requires a bit of power and bandwidth.
Some hubs are amplified, requiring a power source, this
helps but it only pushes the limit a bit.
- Motion Detection software
Download a free
copy of the Webcam Zone Trigger software.
If you have questions about the Zone Trigger
products or if you require consultation and advice on your computer
vision projects, please contact Omega Unfold's technical support:
to motion detection and video capture
to setup a home HTTP server
3 things to check for better motion
Digital Signage How-To
Using Zone Trigger software with the microsoft Kinect
USB bandwidth and connection issues
High-framerate webcams (60-120fps+)