Topic: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Hello Kinovea users,

Recently we started small project (so called ''Falcon eye'') for local Wikimedia (Serbia) and idea is to create kinograms (Diaporama) of various sport activities and sport movements. For this purpose we bought two Logitech C920 HD pro web cameras, we run Windows 7 64 bit operating system. At first use of cameras not possible at high resolution because of drives, when drivers are installed all went fine with one camera, recording runs smooth with resolution of 1024x768 at 30fps. Problem comes when we connect two cameras at the same time, we adjust both cameras at same resolution and fps (1024x768 at 30fps) but fps on both cameras ''goes up and down'', sometimes fps goes over 100 fps at one camera, when we record video (simultaneously record control) with Kinovea (beta 0.8.22) make sort of ''damaged'' video file, you can view it, this is not problem but in some moments video slows down, or speed up or you find some missing frames.

Do you have suggestion how to solve problem? Thanks in advance!
SDCS team

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Decreased resolution at 800x600 at 30fps, and still there is present missing of some frames during simultaneous recording. Do you have any experience with Logitech web camera model C920?

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Hi,
I would say this indicates that the dual recording is too CPU intensive and both playback and recording can't happen in real time.
Can you try with two webcams of different models ? There might be an additional complication with using two cameras of the same model.

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Joan, yes it seams that CPU usage is too high, when there is two Logitech c920 cams on CPU usage is almost 98%, even if machine is enough good 2.4 Ghz and 4gb of ram. I will test how it works with two different cameras. Also I have to check usb ports, seams that they are 2.0 but they act like 1.1

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

As an experiment you can also test the camera simulator (just added in 0.8.22). From the Camera tab, click on "Manual connection" button. In the "Type of camera" combo, choose "Camera simulator" and click "Create camera". Create two of them and go into dual camera mode.

From their configuration you can set them to HD 720 @ 30fps for example, and see if the framerate stays stable, with and without recording.

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Joan, when I open ''Manual connection'' button, in ''Type of camera'' there is only IP Camera, there is no ''Camera Simulator'', I have latest experimental version 0.8.22, do I need to install fresh new same version?

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Today tested cameras at 640x360 at 30 fps, they work like dream, no problem at all, but this is far away from real capabilities of these cameras. BTW, I'm using Toshiba Satellite C655 notebook with 4Gb of RAM and Dual Core processor at 2.2GHz AMD Athlon II P340.

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Experiment done, at HD 720 @ 30fps, before recording fps is stable, when I start with recording from dual mode Kinovea blocks, from that moment I can not stop recording or control any more Kinovea, I have to restart it trough Task manager. I done test at 800x600 @ 30 fps and there is no problem, fps is stable all time before and during recording. Joan, what you suggest?

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

First job done with two web cameras Logitech C920 HD pro and Kinovea software, recording has been done with dual control bar from 0.8.22 experimental version, we made some 250 video files and the most impressive is that we recorder best javelin throw in Serbia in last 10 or more years, made by Vedran Samac from Sremska Mitrovica (79,22m) and one of the personal best shot put throws done by Asmir Kolasinac (20,14m), Serbian national champion. All files has been done in resolution 600x360@30fps

We also used one JVC Everio camera as support but all recording has been done from camera (no use of Kinovea).

Take a look on our work (video resolution reduced for fast upload):


10 (edited by Chas Tennis 2014-Jul-18 17:50:23)

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

The subjects look well framed and attractive.  For 30 fps video playback the videos probably will work well.

However, to examine the frames stop-action single-frame, the limitations on the camera that cause motion blur should be improved. 

Action frame
http://images2.snapfish.com/232323232%7Ffp83232%3Euqcshlukaxroqdfv3%3A68%3Dot%3E83%3A6%3D44%3A%3D348%3DXROQDF%3E285777757%3C257ot1lsi

This frame has excessive motion blur.   The video was taken in overcast lighting conditions as no sharp shadows are showing. [In direct sunlight you will see sharp shadows.]  In direct sunlight, with several times more light, the camera's automatic exposure control may choose a faster shutter and reduce the motion blur.  (I have assumed that your camera does not have a way to manually set the shutter speed.)

The thread Basic Camera Considerations and Cameras has discussion of frame rate, shutter speed and motion blur.   
http://www.kinovea.org/en/forum/viewtopic.php?id=435

How important is stop-action single-frame for your application relative to 30 fps playback?

There are many cameras now that record at 60 fps and have fast shutters, certainly in direct sunlight, either automatic exposure control or manual exposure control.  Especially some recent DSLR camera models will allow manual shutter speed setting.

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Hello Chas,

Thanks for posting here.

Right now stop-action single-frame is not important for us. We are more focused to get routine and skills in practical work with multiple cameras, and than we are have second focus and that is localization of Kinovea in our country followed with education classes and than it comes popularization of open source software and sharing of knowledge. We are more interested to teach coaches, athletes, professors and others how to analyze human movement and that there are cheap tools on the market to do that. In this moment we do not have budget to purchase other expensive cameras, and we like option of dual capturing and fork with two cameras in the same time as well file naming when there is ton of videos you have to do at competition or training.

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

So far for now dual capture with two Logitech C920 cameras works well at resolution 600x300@30 fps, frame rate is stable and quality of picture is good, we tested with prolonged cables total of 7.5m on each camera and no issues at all. We done recordings of various sport movements and all videos can be used for movement analysis. Next task is to solve marker tracking. Also it would be nice if we can get videos at higher resolution we will try with stronger notebook (one we use has dual core processor and 4gb or ram).

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

I spent a few hours on a computer with two Logitech C920 today.

I'm actually surprised you got this far :-)
On the system I tested the highest resolution available was 640x480 and the two cameras couldn't be active simultaneously, only one or the other.

This camera seems to be the current best-seller so I might buy one myself to make more tests and see if its support in Kinovea can be improved.

From what I can gather the higher resolutions are coming down a different channel. There is on-camera compression to H.264 (USB 2.0 bandwidth is about 35 MB/s which is not enough to transmit raw HD frames at 30 fps). Some softwares like Skype must be able to directly consume this H.264 stream. Whereas other softwares handle frames that have been uncompressed by some other underlying component.

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

We used Windows 7 OS and there is control center for Logitech C920 camera, but it supports only one camera. What we have done: first we connect first camera trough usb port we do setting of camera, take it out, connect second camer in other usb port and we repeat settings of camera, and than we connect back first camera, in this way we managed that both cameras has same resolution and frame rate. There is better control center for Windows 8 where you can handle multiple Logitech cameras in the same time but we did not try it, maybe you can test it.

We saw that older computers can not handle dual capture mode easily, we done some videos and frames was missing, than we tested dual capture with better notebook, we did not have super machine but dual core processor, 4gb or ram was enough to handle dual capture with 600x360@30fps. In last 3 months we done tons of videos in dual mode and we like it very much.

There was one issue, if we try to connect both cameras with own cable it makes frame rate goes down, or there is video blinking, or there are lines and noise on video or missing frames, when we extend them with Hama usb-female to usb-male extension cable picture becomes stable. smile maybe we have usb port issue but with cable extensions it works like dream. Also added one more extension in total of 6m (two cable extension of 3m) and it works fine, no issues at all. All recordings we done with Hame cable extensions.

Re: Logitech C920 - Cameras speed (fps) unstable when using two webcams

Thanks for the details.
In the lab I was on they used USB-to-Ethernet extension cables so most of the wiring was inside the walls. It's another alternative for indoor settings.

Regarding multi-core processors it's definitely a game-changer. There are at least 3 intensive threads running in parallel: the image production in the camera driver/grabber, the display of images in the UI thread, and the compression/storage to disk in another background thread. If the CPU has to block any of these to run the others, performances will suffer.

I am making progress on a new architecture that will allow me to better control how everything works together at a low level and making sure the stream of images flows down to the disk with maximal fluidity.