I have just bought a MacBook Air 13" Mid 2011 with 1.8Gz and i7 4Gb Ram 265 SSD
Had choppy HD video 1920x1080 playing thru VLC. The file was .mts-
The fix was VLC->Preferences->input & Codecs->Post-Processing Quality 0 (set it to ZERO)
Have Fun! No more choppy videos