Need webcam with no video lag.

February 6, 2014 at 09:44:00
Specs: Windows 7
Is there a webcam that I can use as a document camera. A document camera is a camera placed above a book or other document and the video is shown on a computer screen. For this application, I need to have little video lag as I want to draw figures with a pen on the book or paper pad. Most webcams claim HD resolution at 30 frames per second but none of them so far can deliver. Any help out there?

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#1
February 6, 2014 at 12:38:23
It is not the camera that causes lag, it is the computer it is connected to.

If the camera claims 30 fps then it is probably delivering 30 fps, but can the computer process 30 fps.

As you give no details of the computer, who can say.

Stuart


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#2
February 6, 2014 at 13:33:05
Thanks for the reply Stuart. I have a Logitech Pro 9000 and have also used a Logitech C920. The computer is a Quad core Intel machine. The unacceptable video lag is the same on all computers. The webcam is a USB 2. If you calculate the bandwidth of USB, it wont handle a HD picture of 1920 X 1080 at 30 frames per sec at 24 bits/pixel. I think all that is possible is about 10 frames per second and that would be OK but not even this is achieved. I am tending to think that no webcams can work and I might have to go to using an expensive SDI camera with the high speed digital interface. The C920 has an onboard H.264 encoder and I thought that might make a difference but it doesn't. I believe that anytime a video stream is compressed, there is a lag that has to be generated. Maybe someday, there will be a USB 3.0 webcam that has the bandwidth.

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#3
February 6, 2014 at 13:58:45
The Logitech C920 is USB 3 ready. All you need is to ensure that you have a USB 3 port on your computer.

Or this:

http://www.amazon.co.uk/Neewer-5pcs...

Stuart


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Related Solutions

#4
February 6, 2014 at 14:13:10
Yes, the C920 is USB 3 ready but it does not operate at a higher bandwidth so I have read. However, I have not tried it in my USB 3 port. This might be a good idea.

Thanks for the link to the other camera . I will investigate it.


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#5
February 6, 2014 at 14:48:37
Any halfway decent computer can handle 1080p/30 video, even over USB 2.0.

Are you using the cameras in a darker environment? If you are, the camera may be lowering its shutter speed, making it look as if the video is being captured at less than 30 fps. Many webcams require a surprising amount of light to work as intended.

DOS/9x Gaming Rig | Athlon 600 @ 672MHz w/ Golden Orb HSF | 384MB | 60GB
Voodoo2 SLI + GeForce 256 DDR | SB Live | Asus K7V | 21" NEC CRT | Win98SE

message edited by jackbomb


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#6
February 6, 2014 at 15:43:45
jackbomb. You seem to be certain of what you say so I would like to continue this discussion.

Tell me, have you actually set up a webcam at 1080p and had the video from the webcam show on your monitor full screen and not have any video lag? I have tried for months and cannot do this. The video lag is OK at 640X480 but not at 1920X1080. If you look at the uncompressed data rate of the video, it is 1.5 gbits/sec much higher than USB 2 can support. The C920 has an onboard video compressor so it should do much better but I do not have any software than can decompress the video to make an acceptable screen display.

Let me explain my application. I want to position my webcam over a pad of paper at a heighth of about 16 inches. I want to be able to view the paper pad on my computer monitor and then be able to write on the pad and see my drawing on the computer screen. This is what is called a document camera. However, when I move my hand, the video blurs.

If you have a solution I would really appreciate it.


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#7
February 6, 2014 at 16:49:01
"Tell me, have you actually set up a webcam at 1080p"

No, because I don't expect brilliant (or even decent) output from a webcam.

The only webcam I have is the 720p integrated camera on my laptop, and even it reduces shutter speed to the point that most video looks as though it's being captured at ~15fps. It does well enough in lots of sunlight though.

"If you look at the uncompressed data rate of the video, it is 1.5 gbits/sec much higher than USB 2 can support."

Well, you'd need DVI or HDMI to transfer uncompressed 1080p video. That's why all USB video devices either (a) make use of an integrated video encoder, or (b) stream video that has been pre-compressed (a USB blu-ray drive works this way).

The video encoder is a fixed-function DSP--it'll have no problem outputting a 10-30mbps 1080p h.264 video stream. If the computer on the other end is less than 8 years old, it should have no problem decoding that stream. However, the optics in webcams are quite poor and usually have trouble capturing HD video in less than stellar lighting conditions. To compensate, they cut shutter speed in half (sometimes even more) in order to make the output video a little easier to see. That reduced shutter speed is what makes the video choppy.

DOS/9x Gaming Rig | Athlon 600 @ 672MHz w/ Golden Orb HSF | 384MB | 60GB
Voodoo2 SLI + GeForce 256 DDR | SB Live | Asus K7V | 21" NEC CRT | Win98SE


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#8
February 6, 2014 at 17:53:28
I evaluated a Logitech C920 and it really did a good job on video quality. It is a highly rated webcam. The autofocus feature sucked however. This cam does have an integrated h.264 encoder thereby lowering the bandwidth required for the USB 2. However, I cannot find any software that will decode the encoded webcam and display it on my computer monitor. I have been told that if the webcam compresses the video, there will be a video lag created and I tend to agree on this but don't know how much. If one is using Skype for example, the video lag is not noticed between the parties at each end. I tutor students via skype and the results seem to be very good. There must be some software out there that will solve my problem unless there is some basic issue I do not understand. I wish i could find a cheap SDI camera with a HDMI output and then my problem would be solved, however SDI cmeras are $$$ for some reason.

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