Video is out of synch with the Tekscan recording

Question/Problem: I have a digital video camera (25Hz) connected via firewire port to my PC. When I record data, the video starts and stops at same time as Tekscan, however when I go to analysis, the video image is out of synch with the Tekscan recording.  If I let the recording play from the beginning, both Tekscan (zero frame) and video (94th frame) start together and finsh together.

Answer/Solution: The synchronization problem you are having here may be because the Start Frame of the video is somehow set to frame 94.  See the image below for how to change this.  See this setting on the lower-left part of the video status bar (1).  The software will remember the last start frame that was set and use this for every new recording.  To reset this to frame 1, you should drag the video cursor back to the beginning of the movie (2).  Then click the Mark Start Point button (3).  This will reset the start point for the video so that frame 1 of the video corresponds to frame 1 of the F-Scan recording.

Because of the nature of the Firewire system (including both the hardware and software), the captured video frames often lag behind the recorded sensor movie even though the two started at the same time.   However, on the same computer, it can be said that the latency of the video is fixed.  That is, once the user determines how many frames of the video behind the sensor movie, the same latency can be applied to the movie/video pairs acquired thereafter on this computer.   The steps in which the user determines the exact lagging video frame number can be called Synchronization Calibration.   Tekscan recommends, prior to capturing data on patients/subjects, you perform a “finger” test yourself -- tapping on the sensor and then synchronizing with the video.  After the initial synchronization is complete, the subsequent data will always have the same amount of latent frames.

To perform Synchronization Calibration, do the following:

1. Record a movie-video pair as described in the Help file, "Recording a Tekscan (*.fsx) Movie and a Video".
   
   
2. Click the Separate Movie/Video button on the main toolbar.
   
   
3. Click the Next Frame button on the main toolbar to advance the pressure movie until first contact is made to the sensor.  This process must be repeated with the video file as well, until you can actually see when first contact is made.
   
   
4. Once you have determined latency on both pressure and video files, click Synchronize.

Synchronizing Externally Captured Video Files

While it is easier to capture video files in Tekscan software as described in the Help file, "Recording a Tekscan (*.fsx) Movie and a Video", the software also has the capability to open video files using external software.  This may be necessary for video cameras without a Firewire link or any other situations where it is necessary to capture video to videotape first which then gets transferred to Tekscan software.

• When recording the video, the trig synch box should be used.  This connects to a LED light that will turn on when the Tekscan software begins recording.  The video should already be recording prior to starting the Tekscan recording.

Follow these steps below:

1. Convert video files to *.avi format. (See also: How to convert .fsx movie files recorded in the Tekscan software into a standard movie format)
2. Open Tekscan software and open the Tekscan movie you wish to link to.
3. Click Open Linked Video button and select the avi file you wish to link.
4. Click the Separate Movie/Video button on the toolbar.  The button will appear as depressed.
5. Use the scroll bar in the video window to scroll the movie until to find the first video frame where the LED is lit.
   • Note: The LED light signifies the beginning of the Tekscan recording.
6. Click the Start Point button on the video VCR button bar.
7. Click the Separate Movie/Video button to re-link the video.  The button should appear to pop out.
8. Click the Play button on the video toolbar to play the movie and video simultaneously.
9. If the movie and video are not precisely synchronized, repeat steps 4-7 until you are satisfied.
10. Scroll the movie until you have reached the start point.
11. Re-save the Tekscan movie.  This will permanently link the movie and video together.

Tekscan, Inc.
307 West First Street. South Boston, MA. 02127-1309. USA
tel: 800.248.3669 / 617.464.4500 fax: 617.464.4266
marketing@tekscan.com


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