Best Of MetaFilter

Cherenkov Cocktail by Apionid (cc by-nc-nd)

2 jiggers of frustration, garnish with a soupçon of rage: help anonymous make the perfect spite cocktail.

You might have seen this video of Mad Men complete with lots of blocky video glitches, dubbed the "bittorrent edition" since you often find downloaded rips of shows and movies carry these sorts of problems. MeFi member Rhomboid breaks down in painstaking detail how bittorrent works, how video encoding works, and what really causes those weird blocks to appear:

Often you'll see a frame suddenly "jump" into full view with a background, which happens when the encoder gets a complete I-frame. This also explains why you'll sometimes see the foreground of the next scene overlaid on the background of the last scene, because again the I-frame that described the scene change was missing but some of the P-frames were recovered