Apple Using Improved Compression Technology for new 1080p iTunes Content
With the introduction of the 1080p Apple TV shows that were recently added to iTunes, an analysis revealed that Apple is using more advanced compression techniques to keep file sizes from becoming too large. The upgraded videos will be supported by the new Apple TV and the third-generation iPad, which is said to pack more pixels than a 1080p television set.
The folks over at ArsTechnica
compared relative file sizes and video quality of 720p and 1080p versions of iTunes content. A quick comparison led them to note that the 1080p versions (1,920 x 1,080 pixels) were roughly 1.5 times larger than their 720p counterparts (1,280 x 720 pixels), despite having 2.25 times the number of pixels on average. It was noted that the limited increase in file size is likely due to Apples support of the high profile for compression of H.264 videos. New High profile decompression algorithms on Apples devices, including the Apple TV, the iPhone, and the iPad, represent an improvement over the main or Baseline profiles used in older devices.
Based on the technical specifications for recent devices, Apple appears to have introduced the High profile H.264 video via its A5 chip. The third-generation iPad, the iPad 2, and the iPhone 4S all support a decoder level of 4.1, which sets a maximum bitrate of 62.5 Mbps for the High profile, while the new Apple TV (which sports a single-core A5 processor) has a maximum level of 4.0 (25 Mbps). Comparing these values to the older A4-equipped devices (the iPhone 4 and the older Apple TV), those devices support H.264 video with a Main profile at level 3.1 (14 Mbps).
In the report though, ArsTechnica
discovered that in some cases, the 1080p version of iTunes TV shows were “pretty much indistinguishable” from the 720p version, although other shows and scenes did show a noticeable improvement with the higher resolution.