Billups article clarification? at

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Canon XL H Series HDV Camcorders
Canon XL H1S (with SDI), Canon XL H1A (without SDI). Also XL H1.

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Old November 30th, 2006, 11:59 PM   #1
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Billups article clarification?

I was reading an article called "Scott Billups Tests Canon XL H1" from a competing site, so I don't want to provide a link.
In this article there is this quote which I do not understand, as well as never read any where before.

"The XL H1ís true 25Mbps segmented-frame signal packs 50 Mbps into each frame on tape while the SDI signal is a whopping 1.2Gbps."

50 Mbps huh?
Damnit Jim, I'm a film maker not a sysytems tech.
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Old December 1st, 2006, 06:53 AM   #2
Obstreperous Rex
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No problem with the link -- it's

Billups wrote that article back when Canon USA was still in the "we will neither confirm nor deny" stage regarding Frame mode and how it works, so everything written about it back then (the article is from May 2006) was at best merely well-intentioned speculation.

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Old December 1st, 2006, 09:43 AM   #3
Barry Wan Kenobi
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Obviously it's not phrased properly; of course there's not 50 megabits of information in each frame on tape.

Two ways you could look at it -- if we're talking about how much room each frame takes up on tape, you could simplify it by saying each frame is about 1 megabit, but that wouldn't be accurate because of the long-GOP nature of the encoding; the first frame in the group might take up substantially more space and then every following frame of the group takes up substantially less space.

The other way to look at it is, he might have been saying "since the HD-SDI signal is 1.2 gigabits per second, and there are 24 frames per second, each frame holds 1200/24 = 50 megabits of raw uncompressed information.

But I don't know why he would bother trying to spell that out, because it's completely irrelevant when it comes to what's on the tape. On the tape, each frame averages out to be about one megabit, not 50.
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