To playback HD 1080i Quality Mp4s on a high end pc - use CoreAVC Pro Codec. It took some researching newsgroups to discover this detail! - Use Lock/Auto-Manual Focus mode, use 720p mode.
Outstanding VIDEO At 720p resolution. 1080i playback is smooth on my Intel Quad Extreme; Uses compressed mp4, Focusing is weak; I use Semi-Manual Focus for outstanding results. NOT for a beginner.. Get a Canon HG10 if you are looking to go High Def.
You need a very high end PC to Play back 1080i .mp4s I always use and recommend to use 720p MODE which does 60 Frames per second unlike 1080i which is 60 FIELDS (aka 30 FPS) .; Unless you use the included Editor, the FOOTAGE does not work with: AVID LIQUID 7, Adobe Prem., Pinnacle Studio, etc..