Apple TV: The Real Video iPod

Ian Hobson - 10:29am Mar 31, 2007 PST
Guest User

I think Jeff writes a very fair and balanced review of the AppleTV.

However, when he states:
> (A feature-length movie purchased from the iTunes Store is about
> 1.5 GB, while HD content would be about 16 times larger than that.)
I don't believe that's necessarily correct.
AFAIK (we can't get them in the UK), the iTunes movies are of 640 x
480 resolution today. Using 1280 x 720 resolution (considered HD
resolution) in fact gives a pixel count exactly 3 times that of the
standard VGA resolution. Even 1920 x 1080 HD pixel count is only
6.75 times and AppleTV cannot support this today. Of course the
frames per second comes into it as well. But movies are typically
filmed at 24 frames a second, so it is perfectly fine to have 24fps
as HD material.

So, assuming no efficiency benefit (or negative) from compressing
larger files (or use of a different variant of the H.264 codec), the
video part of the files would be anywhere from 3 to 6.75 times larger
(and the larger ones would require shrinking down again to be played
via an AppleTV).

But that's not all. Sound makes up quite a large part of the file.
This would not change on HD, so in fact file size for HD is likely to
be in the range perhaps of 2.5 times (rather than 3) - still a
potential problem if you want to watch in near-realtime for many
users depending on their broadband connection.

One potential add-on with HD material might be true 5.1 sound, which
would perhaps increase the file size. There have been many comments
dinging AppleTV about this, when they're basically misunderstanding
the issues. There have been a few articles pointing out that for
movie downloads (as opposed to DVDs) it is only appropriate to use
AAC for 5.1 sound (AAC of course is a format that Apple has been keen
to promote). Use of AC-3 is not appropriate partly due to size and
inefficiency. But there are currently almost no surround sound
systems supporting AAC 5.1, so the playing devices (AppleTV) would be
forced to do what they do today (or perhaps create an AC-3 output on
the fly which is quite demanding, and would require licensing).
Apple's choice of H.264, AAC, and general adherence and adoption of
MPEG 4 standards, will put it in good stead going forward. The
analogy perhaps is to compare it to iMacs not having 3.5" disk
support - they are trying to move things forward. Apple will
undoubtedly shift towards multi-channel AAC (for which Dolby was a
main proponent) as soon as it makes sense to do that, and the AppleTV
(and indeed all other macs which are equipped with optical outputs)
are ready for that change.

Regards
Ian