It is possible that when capturing to AVI format that frames will be dropped MJPEG compression is used and set at 100%. 100% quality results in a very high data rate. This can only be done on drives that are capable of a high sustained write data rate and that are relatively non-fragmented, otherwise frame drops are possible. This setting is only possible if the Custom preset is selected. If you notice dropped frames in this situation, lower the quality percentage to 90 or 95%.