30-second previews use RTMPT protocol indeed. I don't see any sense downloading or capturing them, but you need 30-second previews, see the following:

FAQ: How to record/download/capture/save Adobe Flash .FLV video RTMP stream from embedded player
How to record rtmp:// flash video .flv stream from embedded Adobe Flash Player
RTMPE stream recording/downloading/capturing/ripping/saving