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vectorburn
Member
Joined: 29 Dec 2004
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ok - a little history:
as far as video on an ipod, and especially wanting to crank out the best for tv,
ipod 5g resolutions:
h.264: 320px*240px - max. period.
mpg4: 480px*480px - with that catch that this is a total product dimension.
explanation (in 4:3 terms):
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480*480 (w*h) = 230400px^2. as long as your dimensions (w*h) multiply to </= (less than or equal to) 230,400px^2, you can use other resolutions (and better).
so, anyone knowing simple math with recognize
480px:480px (what apple says) = 1:1 (square, not much use).
4:3 = 512px:384px,
512px*384px = 196,608px^2,
196,608px^2 </= 230,400px^2...
this is better than
4:3 = 480px:360px,
480px*360px = 172,800px^2
172,800px^2 </= 230,400px^2
(with the added rule of keep everything nice and neat with the divisible-by-16 macroblock...)
note that the next step up
4:3 = 576px:432px
576px*432px = 248,832px^2 and
248,832px^2 is not </= 230,400px^2
so, 4:3 theoretically caps, for 5g resolutions at 512px*384px (w*h)
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and an explanation (in 16:9 terms):
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from above:
480*480 (w*h) = 230400px^2. as long as your dimensions (w*h) multiply to </= (less than or equal to) 230,400px^2, you can use other resolutions (and better).
so, let's go with
16:9 = 640px:360px, and while
640px*360px exactly = 230,400px^2, it breaks the divisible-by-16 rule:
640/16 = 40 (whole number, cool).
360/16 = 22.5 (not a whole number, uncool).
so, saving you some trial and error or extra math:
16:9 = 512px:288px
512px*288px = 147,456px^2
and this pacifies the
147,456px^2 </= 230,400px^2
and 147,456px^2 is better than
480px*270px = 129,600px^2
and, unfortunanely, the next up, 768px*432px, doesn't come anywhere near being in the right range (331,776px^2)
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and obvious, 2.35:1 dimensions and more will follow this similar trend).
now:
ipod 5.5g resolutions (5g's can play with firmware update):
h.264: 640px*480px
mpg4: 640px*480px
now, from my brief experimenting (and very lengthy) with 5.5g h.264, it would appear no matter how you do the dimensions, nothing wider than 640 will work (i tried 656, and would not move over to my ipod, and yes, the ipod is 5.5g; also tried 624 wise, and it worked as well)...
now, for my question:
does mpg4 x640 suffer the same limitation as h.264, in that no matter what you do, you can't get wider than 640?
my math:
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640px:480px is 4:3, so you can't do better than that.
but, if the prior 480px*480px rule carries over, we can get a little bit of benefit for widescreen and anamorphic...
640px*480px = 307,200px^2. anything under this amount, if this theory proves true, should work.
so,
16:9 = 736px:414px
736px*414px = 304,704px^2, and
304,704px^2 </= 307,200px^2 |
so, does the old rule still ring true?
will a 736px*414px video work on my video ipod? (max that res out a bit more...)
(i could experiment, but i figure there's someone with a more definitive knowledge that knows and can shed light on this mystery math.
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GMaq
Linux Member
Joined: 17 Mar 2004
Location: Canada
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rumplestiltskin
Member
Joined: 15 Jun 2003
Location: United States
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The smaller H264 spec is not "320x240 max.period". It is 76,800 pixels in whatever dimensions using the rule of 16's. 368x208 is a perfectly valid set of dimensions that drop into the iPod and play just fine. (No, 656x112 I haven't tried.)
I assume you want >640 width for the LC (low-complexity) encoding because you have a wide-screen TV?
I haven't tried anything wider that 640 as I have only a standard format TV. If >640 width doesn't work, it's probably because Apple is not yet ready to make that jump. Remember that they are still trying to put into place all the partnerships they need for a truly successful movie store. If they jump the gun and permit >640 pixels, some of the studies may balk. Of course, once the partners are in place, expect a wide-screen (6G?) iPod and the iTV.
It's funny but it may be Apple that really drives the adoption of wide-screen TVs. (Of course, your Mac already has such a screen so the golden convergence may center around the 24" iMac (and the 30" unit that's coming late next year). 
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vectorburn
Member
Joined: 29 Dec 2004
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thanks for the correction and insight.
gmaq, i will give mpg4 a whirl...
vb
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