time discrepancy between Tobii and .avi files

Hello help forum,
When downloading oral reading (reading out loud) eyetracking data from Tobii Pro studio and comparing to converted .avi files (Audacity, voice from reading out loud)) there is a time discrepancy in total duration of a recording. For example: Tobii pro time stamp info for 1 reading sample is 2:24 minutes. When the same reading sample is viewed via Audacity the sample is 2:22 minutes. This discrepancy is consistent across participants and reading passages. Is this discrepancy introduced by file conversion, perhaps? Or maybe by change in sampling rate? We would consider any help with this before analysis of this data.
Thanks, Inge

It could be a problem with the original file or it could be a conversion problem. There are time codes in some audio/video files and sometimes those can cause trouble… I’ve had MPEG-2 files that get “lip sync” errors after editing or format conversion with a video editor.
the highly-compressed formats seen to be more prone to this than the less-compressed or non-compressed formats.

It’s not a sample rate error. You’ve got about a 1% error and 44.1/48 is almost 10%.

MP3 (and I think AAC) will add a few milliseconds to the beginning and end, but you’re problem is worse than that.

The actual playback time can very a bit, due to the electronic/physical clock in your soundcard (which is never perfect). If the software doesn’t show any difference but there is a difference in the “real world”, there may be a clock mismatch between your recording and playback hardware.

But, the digital time in Audacity (after conversion/decompression) depends on the sample rate and the number of samples and that’s a fixed-mathematical number and Audacity will do that simple calculation perfectly.