I am using PRE 8 to edit videos and post them to you tube or put them on dvd's. My Gopro video camera records in MP4 and the videos come out great on You Tube. My JVC GZ-HD300BU records in AVCHD and when I edit them using PRE 8 and post them to youtube the video quality is poor. The video is choppy and does not playback smooth while I am edditing it in PER 8. Also I am recieving a worning that states "display performance will be poor due to incorrectgraphics card or drive"
Can you give us some more info, especially your graphics sub-system, with the card make/model and the driver version and date? This ARTICLE will also be useful for giving tips on other info that can be very important.
For tips on YouTube, this FAQ Article will provide some tips.