Apple has ushered in 1080p video across iTunes after announcing the third-generation Apple TV which offers full, high-definition streaming.

Despite concerns about file sizes with the increased definition from 720p, ArsTechnica has an overall examination of how 1080p iTunes video looks good and saves space while using better H.264 compression.

The site examined two free episodes of shows – “The Big Bang Theory” and “Awake” – to try to gauge the difference between the picture quality of 720p vs. 1080p.

First, while 1080p video contains more than 2.25 times as many pixels as 720p, the file sizes in iTunes are not very different. Apparently, on average, the 1080p video is around 1.5 times as large as the 720p counterpart.

But the results were a little mixed on how much better the 1080p video looks. In “The Big Bang Theory,” there wasn’t all that much different between the two files, except for examples like the bottle in the pictured clip.

In “Awake,” the results were somewhat more apparent, with brighter scenes looking better in 1080p.

According to the examination, the reason 1080p video looks better without a massive increase in file size is due to some of the technical specs of the new Apple TV and iPad.

“The AppleTV now supports H.264 compression for 1920×1080 resolution video at 30 frames per second using High or Main Profile up to level 4.0, the iPad and the iPhone 4S the same up to level 4.1. The profile indicates what kind of decompression algorithms the H.264 decoder has on board-the “High” profile obviously has some tricks up its sleeve that the “Main” or “Baseline” profiles known to previous devices don’t support. The level value indicates how many blocks or bits per second a device can handle.”

Currently, only the iPhone 4S, the new iPad and the new Apple TV will support 1080p video.

Have you downloaded any 1080p video from iTunes yet? Have you noticed a big difference from 720p?