Im using the Add Video option for extracting frames from some videos off a Go Pro Hero 5. When i type in to extract say every 10th frame it will give an estimate of the number of frames that will be produced. Tis number is drastically different to the number of frames that get produced. I also end up with a large number of duplicate (identical) frames from the first couple of seconds of the video.
As can be seen from the attached log, it estimates 42 frames and i got 216. (Probably 50 or so were duplicate frames)
Next it estimated 81 frames and i got 419 (100 or so were duplicate). And so it goes on