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Infinite Loop / The Apple Ecosystem

iPhone, iPod touch support 720×576 rather than 640×480 video

Apple has been fibbing about the video resolution supported on the iPhone and …

This weekend, I finally got around to watching my first movie rented from the iTunes Store: Punch-Drunk Love. According to the Internet Movie Database, it was filmed in Panavision, which makes the aspect ratio 2.35:1 and requires a good bit of squinting to make anything out on the iPod touch. These very wide aspect ratio movies are annoying, because they don't make very good use of the maximum 640x480 that Apple specifies for iPod/iPhone-compatible content. In order to arrive at the 2.35:1 aspect ratio, the picture would have to be a paltry 640x272.

However, according to iTunes, the movie was actually 853x366. Yes, that's right: Apple says the iPhone and the iPod touch support a resolution of 640x480, and then it produces much larger video files that play just fine.

Some further experimentation shows that the iPhone and the touch will play files of up to 720x576 at 25 frames per second—coincidentally, the exact same size at which PAL DVDs are encoded. Files up to this size can played through mobile Safari or synced through iTunes.

However, that doesn't explain the 853x366 Adam Sandler movie. The solution to that mystery is probably also found in the DVD world: anamorphic encoding. NTSC DVDs are always encoded in 720x480, which has an aspect ratio of 1.5:1. However, they're played as 1.33:1 (4:3) or 1.78:1 (16:9) if the content is encoded as anamorphic widescreen. And, apparently, the iPhone and iPod touch are capable of playing anamorphic encoded video files. So my guess is that the movie I rented was encoded as 720x366 with an anamorphic aspect ratio of 1.78:1.

Obviously, using a higher resolution than what the screen supports (480x320) isn't all that useful if you just plan on watching video on the iPod touch or the iPhone, but it can be if you want the same files to be playable the mobile device and on the computer screen or TV. If you are interested in experimenting yourself, don't forget to stick to baseline H.264 encoding and remember that these files will not play on older generation iPods.

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