Video Mathematics

I thought it would be good to list some of the formulas that video editors should know. I edit and hardly ever consider the math and i am sure there are others just like me.

Recently a broadcast editor told me something like, " The file size when you in code is simply the bit rate times the current file size."
I don't believe this to be true due to the resolution variable.

I might guess it to be file size x bitrate and then something with the intended output resolution. which means i couldn't do the math to get within 25%.

In a recent thread about an odd resolution for broadcast, someone said that the number 810 was not divisible by 9 so it wasn't a true 16:9 aspect. That was my first time hearing anything like it.


So what are some of the formulas that an editor should be familiar with?

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

formulas like:

aspect math
resolution math
conversion math
color space


This almost should be in a wiki. Doesn't have to be everything just some basics to keep in mind.

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

Y = R * 0.299 + G * 0.587 + B * 0.114
U = R * -0.169 + G * -0.332 + B * 0.500 + 128;
V = R* 0.500 + G * -0.419 + B * -0.0813 + 128;



www.strypesinpost.com

Oh, cripes, now you've got them astericking...

- Loren

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i know it;s not what you mean, but here you go anyway:

[en.wikipedia.org]

According to Walter Murch, when it comes to film editing, there are six main criteria for evaluating a cut or deciding where to cut.
They are (in order of importance, most important first, with notional percentage values.):

Emotion (51%) ? Does the cut reflect what the editor believes the audience should be feeling at that moment?
Story (23%) ? Does the cut advance the story?
Rhythm (10%) ? Does the cut occur "at a moment that is rhythmically interesting and 'right'"
Eye-trace (7%) ? Does the cut pay respect to "the location and movement of the audience's focus of interest within the frame"
Two-dimensional plane of the screen (5%) ? Does the cut respect the 180 degree rule?
Three-dimensional space of action (4%) ? Is the cut true to the physical/spatial relationships within the diegesis?

Murch assigned the notional percentage values to each of the criteria. "Emotion, at the top of the list, is the thing that you should try to preserve at all costs. If you find you have to sacrifice certain of those six things to make a cut, sacrifice your way up, item by item, from the bottom."

--------------------------------------------------------


the same link also references interesting ideas from Edward Dmytryk (with no numbers, sorry )

Edward Dmytryk stipulates seven "rules of cutting" that a good editor should follow:

Rule 1: Never make a cut without a positive reason.
Rule 2: When undecided about the exact frame to cut on, cut long rather than short.
Rule 3: Whenever possible cut 'in movement'.
Rule 4: The 'fresh' is preferable to the 'stale'.
Rule 5: All scenes should begin and end with continuing action.
Rule 6: Cut for proper values rather than proper 'matches'.
Rule 7: Substance first?then form.


cheers,
nick

[Rule 5: All scenes should begin and end with continuing action.]

Except where they shouldn't.

And I would only add to that auspicious list:

Rule 13: There is no such thing as a quick cut.


- Loren

Today's FCP 7 keytip:
Nudge a Canvas layer by SUBpixels
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2 + 2 = 5

Quote
Loren
"Rule 5: All scenes should begin and end with continuing action.
Except where they shouldn't."

yeah, that is an odd one, and you've pretty much hit the nail on the head, there, Loren!


Rule 4: The 'fresh' is preferable to the 'stale'.

is interesting. it works on many levels.

within a dialogue scene, say, back & forth cutting gets pretty boring. hopefully you have to coverage to make it less so,
obviously its better if the director has thought it though and has good coverage, and more to the point, good blocking,
so you don't get repetitive shots.

in the big picture, you don't want repetition either.
keep the story moving, advancing.
don't tell me something i already know (unless you can slip it in very discretely)

i've read Dmytryk's book, and he also talks about this "rule" in the micro sense.

talking about the minutia of editing, he suggests that if you need to "roll" an edit (not his terminology)
that you should always roll it to make the edit happen earlier.
he prefers the "fresh" new shot to hanging on the "stale" old one.

not always 100% true, but worth keeping in mind.


Rule 1: Never make a cut without a positive reason.

yeah! this is a clearer statement of one my personal rules, regarding "cutaways", a term i don't much care for.
"Don't cut away, cut TO"



cheers,
nick

> within a dialogue scene, say, back & forth cutting gets pretty boring. hopefully you
> have to coverage to make it less so

That's a double-edged sword, though. I just saw The Expendables. Really ADD editing and show-offy shooting and lighting. Couldn't tell one character from another in those final action scenes except from the sound of one guy's gun. Too many new shots take away from our ability to ground ourselves in the scene. When a scene really works, a dramatic scene (eg. the train-station scene in Sophie's Choice) or an action scene (eg. the final fights of Drunken Master II), overuse of coverage backfires. The Pixar guys are very good at this. With their almost unlimited ability to create new shots and coverage (since their world and physics are already made), they actually use a lot of long takes...and they never try for the tired "wobbly camera" for action scenes.

The "continuing action" thing is not a good rule. It doesn't take context into account. It's often good to open static. On an early student film, an instructor kept telling me to not let the main character clear the screen as he walks off. But it never felt right, so I trusted my gut. It was the end of Act 1 and the next scene was extremely different, so I let him clear the frame to reset the audience psychologically. You may not notice within the flow of the story (it's about 15 frames' difference), but you feel it.

> this is a clearer statement of one my personal rules, regarding "cutaways", a term
> i don't much care for.

I might have the same psychology. I never say "cutaway". I say "insert". Makes more sense.
"Cutaway" does have one logic behind it. Sometimes the way to refresh a shot you've seen a lot is to cut away from it, freeing up the tool of choosing the right time to cut back to it and renew its impact.


www.derekmok.com

I do like and respect Walter's 6 reasons for any cut. I've boiled it down to three, but the other three are implicit. Eye Trace in particular is sexy.

- Loren

Today's FCP 7 keytip:
Nudge a Canvas layer by SUBpixels
with Command-Option with Arrow keys !

Your Final Cut Studio KeyGuide? Power Pack.
Now available at KeyGuide Central.
www.neotrondesign.com

I found this a few days ago. Its very wide.

[neuron2.net]

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"