MSP:Preferences:Edit:Frame type ??????

[v2rahn]

A simple question:
What do I have to select in MSP5.2 under File:Preferences:Edit:Frame type ?? Is it Frame-based, FieldOrderA, or FieldOrderB ?

I capture PAL from a camcorder with a Marvel G400TV ?

If more than one setting is possible, what to use when and what are the implications ?

I have even more questions, but I'll keep them separated, for the sake of overview... Thanks very much for all your replies to this one.

Stephen

[fluggo99]

Field Order B for a G400TV.

[Fred H]

Hi,
maybe its a dumb question, but what's the difference?
I have a Marvel G400-TV using the Frame-Based selection, just because I don't know what they do & which one is the best for what

[fluggo99]

NTSC TV isn't 29.97 frames per second, you know. And PAL TV isn't 25 frames per second. They're 59.94 and 50 separate fields per second, each field representing a completely different instant from the one before or the one after it.

The clever folks that devised the system figured that what they should do is interlace the two fields, reducing the huge volume of data simply by having each field represent a different part of the picture. In one sweep, all the even-numbered lines on a TV would be hit with the first field, and while those phosphors were still fading, a second field would be drawn to the odd-numbered lines.

So we've got smooth motion. Now, when we got to computers, it became convenient to think of video in frames instead. After all, every pixel you see on your monitor is supposedly from the same instant in time. (Yeah, there's technicalities, but let's ignore them for now.)

When we want to capture video, we don't organize it in terms of the original fields; we combine consecutive fields into one picture. In a 704x480 capture, lines 0, 2, 4, 6 ... 480 all represent one field, and lines 1, 3, 5, ... 479 all represent a different one. It's like meshing your fingers together-- every other finger is from one, complete hand, and the others come from another separate, but complete, hand. Unmesh the fingers, and you have the original two components that made the mix.

When converted back to TV, they're separated back into their normal field specs-- but to any program that tries to read them, they look like a single frame. Your software won't know the difference between frame-based video and field-based video unless you tell it.

Field A and Field B tell your software which lines are supposed to represent the first field in a picture, and which the second, so it can keep everything in its proper order in time. Field A, I believe, tells it that the even-line picture comes before the odd-line picture, and Field B tells the opposite.

Telling your software you have frame-based video usually doesn't hurt because it won't mix the rows into the wrong order. In fact, it's often beneficial, because frame-based rendering is MUCH faster.

Whew! Now, on to what I'm supposed to be getting paid for...

--fluggo99

[This message has been edited by fluggo99 (edited 07 March 2000).]

[Fred H]

Thanks, fluggo99 for the very comprehensive explanation.
Now I completly understand it.

[This message has been edited by Fred H (edited 07 March 2000).]

[v2rahn]

Thanks for the good explanation !
Stephen

[fluggo99]

Yo! Just thought of a cool demonstration for you guys.

1. Fire up Video Capture, and set it to overlay.

2. Play one of your captured MJPEG files. Video Capture's taken over the hardware, so the software has to decode it for you. In the interest of time, it just displays the file as-is. You should be able to see all the different field lines, especially if you're watching a high-motion video.

[Fred H]

Here is a text I found in the Matrox VT readme.txt:

"...- If you're using a video editing program that lets you select a field
order for video editing, select field B (the second field). If you use
field order A, you may notice problems with transitions between clips or
special effects. For more information, see the documentation for your
video editing program...."

fluggo99, without your fine explanation I've never thought abot this