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H264 and who's Army?

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Lance Wilhoite
H264 and who's Army?
on Jun 23, 2008 at 5:45:11 pm

Does anyone know how Apple posts these HD trailer, like http://www.apple.com/trailers/sony_pictures/hancock/hd/ and have them turn out to be 1:45 in length and ONLY 211mb?

Of course they are H264. But what pre-processing is done to get it down to that size?
Sometimes the QT player flattens the movie before playing.

REALLY gots to find this out. Anybody got any ideas?

L



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Daniel Low
Re: H264 and who's Army?
on Jun 23, 2008 at 6:56:58 pm

There's no magic to it.

Apple get hold of the best quality source available. Better than most of us can get access to. They have a skilled team of compressionists using a variety of tools (I hear that they still use cleaner as well as compressor) and they use preprocessing tools to the full effect, tweaking for each clip, unlike most people out there.

That said, I don't think they have done as well as they could have with this clip, the blacks aren't black!





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Lance Wilhoite
Re: H264 and who's Army?
on Jun 23, 2008 at 7:41:51 pm

Hey Daniel,
Thx for responding. I'm a VFX Supervisor and have full ap scans of our finished negative for Ghost's of Mars as well as TIFF HD frames for lots of my Showtime Projects. I'm trying to create a demo reel in QT.

I'm wondering if they selectively reduce the bit depth for each sequence before compressing, similarly to log to lin conversion with Cineon files. Dunno... But I GOTTA get a handle on this.

Lance



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Daniel Low
Re: H264 and who's Army?
on Jun 23, 2008 at 9:01:34 pm

If I knew the exact low-level details, I certainly wouldn't post them here!

Obviously if they have 10 or 16bit source there'll be a down sampling to 8bit somewhere along the way, along with some Gamma correction and in special cases (i.e high value productions) manual colour correction and some selective segment re-encoding, I would have thought.

'Ghosts of Mars' will probably be a difficult challenge as (as far as I can remember) it's very dark and rather grainy, as such, managing the grain and retaining shadow detail without blowing highlights will be difficult.

If you are interested in squeezing the best from H.264 (or X.264) and want to understand the best workflow with high-end material, I think you'll find the experts at forum.doom9.org most knowledgeable.


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Please post back saying what solved your problem. It could help others, and saying 'thanks' is free!


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Chris Borjis
Re: H264 and who's Army?
on Jun 25, 2008 at 11:33:13 pm

one major factor that helps to get the size down is multi-pass vbr encoding.
(but you probably already know that)



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Kris A. Wotipka
Re: H264 and who's Army?
on Jun 26, 2008 at 4:50:05 pm

Manually dropping in Iframes where they are needed will help on file sizes as well. Unless you really know what you are doing, be prepared for several renderings to get everything tweaked right for file size vs. temporal quality.

kris@wotipka.com
Image maker


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Lance Wilhoite
Re: H264 and who's Army?
on Jun 26, 2008 at 5:07:04 pm

Thanks Chris and Kris and Daniel.
I'll research further. Multiple VBR passes is likely only the beginning. When I shot the explosions for the train sequences in Ghost's of Mars, we really did shoot a shallow depth of field. we were afraid the flash from the explosions would light and expose the seams in the black cyc. as a result we did get a grainy dark negative. But that's what John wanted.
I'll let you know if I make any headway with this compression issue.

Lance



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