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Topic: DVD playback on Blu Ray player

Joe Redifer
You need a beating today

Posts: 12859
From: Denver, Colorado
Registered: May 99

posted 03-24-2009 12:14 AM

*Topic hijack*

I once e-mailed a news station telling them that stretching 4:3 video to fill the 16:9 area was bad form and very unprofessional looking. They responded that it is their policy not to do that and it is simply something they don't ever do. I responded by e-mailing them stretched images captured from the next evening's newscast complete with overlaid graphics which weren't distorted (so I couldn't be faking my images). They replied (in an almost frustrated tone) that they did that for "artistic effect". So I told them that they were right. They never stretch the image... except when they do. Brilliant!

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John Hawkinson
Film God

Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002

posted 03-24-2009 03:25 AM

Julio wrote, "I wonder how many non-sync mechanical projectors run at exactly 24fps as oppossed to say 24.3 average (or 23.8) [uhoh]"

Argh! What kind of a question is that? Do you mean 24.0 fps versus 24.3? Or do you mean 24.00 fps? 24.000 fps?

My experience is that you will find quite a lot that are running at least 0.1 fps fast or slow. I would guess, say, 20%. For instance, on Century with a poly-V-belt, you can get 0.1 fps just by varying the belt tension. (I assume it's a lot better on newer Centuries with timing belts, and other timing belt projectors).

[ Note that, also, on projectors with async motors, it's conceivable that the line voltage varies enough to affect the running speed of the motor by a teensy bit, but enough to hit 0.1fps. Of course this depends on your motor and how much line voltage variation there is [time of day? etc.] ]

Scott said, "I shot part of the screen with a 16mm camera with a crystal-controlled motor (should be accurate to +/- 1/4 frame over ten minutes or something like that). There was no flicker at all, suggesting that the projector (Century on RCA soundhead) was running at dead-on perfect 24fps."

I don't think that's clear. Let's say your camera is 24.0fps and the projector is 24.1fps. Dare I ask your shutter angle?

Anyhow, that means that the projector is just a bit faster, and at the end of the first frame, it will switch to the second frame just a bit before your camera does.

24.0fps is 41.66ms. 24.1fps is 41.49ms. 4166 and 4149 are relatively prime, so that suggests every 1728.4ms (1.7 seconds),
you miss a frame. But will this manifest visibly as flicker?
For one thing, every 2 seconds is pretty slow, so an occasional flicker at that frequency may not be visible. For another thing, if it all happens in the pulldown (or when your camera's shutter is closed), you may not see it either.

If the two frames the projector is switching between are similar (which of course they will be most of the time), you might not even be able to detect an anomaly, were there even one present.

It's not like filming an NTSC television where there are continuous phenomena, so you see rolling bars/strobing.

--jhawk

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