Recorded video: frame rate accuracy?

[ben_v]

I'm trying to sync sensor data with video recorded from a USB camera using frame number--the current video frame number according to NI Vision Acquisition Express is recorded with each sensor data sample. When the .avi file is created to start recording, the frame rate is set to 10 frames per second. However, as I watch the instantaneous frame rate from output from the NI Vision Acquisition Express VI the frame rate varies depending on the brightness of the scene viewed by the camera. I understand that when the brightness of a scene increases, the camera circuitry decreases the exposure time which increases the measured frame rate. However, I need to know that the frame number output by the NI Vision Acquisition Express VI (and recorded to the .lvm) corresponds to the frame number of the video when viewed in an application like Quicktime or VLC.

I've attached the VI in question.

Thank you

[David-A]

Hello ben_v,

The Frames Per Second input to the IMAQ AVI Create VI specifices the playback rate, not the recording rate.  This means that regardless of what rate you are capturing images and placing them into the AVI file, when you open the AVI file in a media player it will playback at the rate set by the Frames Per Second input. 

http://zone.ni.com/reference/en-XX/help/370281M-01/imaqvision/imaq_avi_create/

David A