Video conversion: iPod vs Apple TV format | iLounge Article


Video conversion: iPod vs Apple TV format

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Q: I’m using EyeTV 2.4 and an Apple TV and am wondering if there is really any advantage to converting standard definition TV shows using the “Apple TV” setting instead of the “iPod” setting. They look the same to me either way, even though the Apple TV conversion produces twice as large of a file, so what’s the point?

- Eric

A: In reality, there is probably little difference in converting most standard broadcast TV content for Apple TV versus iPod, although this may be somewhat dependent upon the source material.

Standard North American television signals use 480 visible lines of screen resolution (which is what the “480” represents in 480i and 480p video standards). While analog TV signals do not have a concept of horizontal resolution, a standard television show when recorded onto a computer will produce a 640x480 resolution frame size.

You’ll note that this is the same resolution as the video format supported by the iPod itself, which means when you’re converting a video for the iPod using any of the more recent conversion tools, you’re getting a 640x480 frame size anyway (although we should note that some older conversion tools may still use the older iPod format of 320x240).

Although the Apple TV supports resolutions of up to 1280x720, if your source material is still only 640x480 (which any standard definition TV broadcast will be), then the converted video will still only be 640x480, since none of the existing conversion tools will actually do any kind of up conversion on the video.

Therefore, no resolution is gained by converting to Apple TV format. What does increase, however, is the bit-rate of the video stream. The Apple TV is capable of handling more than twice the bit-rate that the iPod is, and video converted to Apple TV with most encoders is encoded at bit-rates of up to 3000kbps. Whether or not this makes a difference will be entirely dependent upon the source material, and most analog TV content are not going to benefit from a higher bit-rate. In our own tests with newer shows from some of the better analog TV stations, the higher bit-rate resulted in slightly smoother video playback, however these differences were not really noticeable except under close observation.

One other factor to consider when encoding content is whether you actually want to watch it on your iPod. Naturally, content converted for Apple TV will not be viewable on the current line of 5G iPods, although we’re certainly hoping that Apple will raise the bar in this area with the next generation iPod model.

However, the bottom line is that if you’re encoding content from standard definition TV broadcasts, there is probably very little advantage in converting this content for Apple TV versus iPod, particularly when you consider the additional storage requirements for the larger files.

Note that this does not apply to DVDs, however. Even a standard-definition DVD will benefit greatly from the higher bit-rate available on the Apple TV. Further, since most standard-definition DVDs are in a widescreen format, you’re actually only getting a 640x360 image in iPod format due to the aspect ratio, which is a reduction in the overall DVD resolution (720x480). On the other hand, the Apple TV format will take advantage of the full resolution of the source DVD (720x480), and encode it with a higher bit-rate. Although the differences were still not dramatic (particularly in light of what the Apple TV is actually capable of), it made enough of a difference in our own tests to sacrifice iPod viewing compatibility in favor of the better output quality on the Apple TV.

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