Whenever I play 1080p films such as Avitar in 1080p in VLC, it's fine for a few seconds, but then freezes and jumps around before getting back on track, then repeats every 10 or so seconds....
Try Movist, it is much better in handling HD content embedded in the .mkv container/format.
You could also try VideoSpec (I prefer that, though it hasn't been updated since 11/2009), MediaInfo Mac (10/2010) or MediaInfo (10/2010, there is a Mac OS X version to download, VideoSpec and MediaInfo Mac are using the same library as MediaInfo) to analyse the file and post the report here.
There are a few other threads about VLC on the MBA. Apparently VLC hasn't been updated to use the GPU to help decode video, which would explain why the 11's slower CPU might cause stuttering.
Players like Plex that have been updated to use the GPU do a much better job.