N860CR

Hi everyone. I have a Samsung SDR-1656 DVR that runs 12 cameras. I needed to backup some footage onto a USB for the police this week (first time I've used the backup function) and found that the footage (about 2 hours long) was broken up into multiple (ie hundreds) .AVI files of varying length. Some were only about 10 seconds, others were a few minutes. This obviously makes the whole process a bit annoying as I then have to merge the files together to create a single .AVI which takes forever (and, of course, several fail). When looking at each individual file, it does seem that the resolution is different in each and this might be what prompts the creation of a new file. EG: The file 1 might play in a screen half the size of file 2 and then file 3 changes back etc etc. Any idea what might be causing this? I can't see anything obvious in the settings. Thanks