newb - smooth scrolling credits in AE ?

People have different formulas, but the thing to remember about credit rolls is that you don't want to create a stroboscopic effect with the text. It's all about how far the letters move per frame. 

In practical terms, you want to move text no more than the width of the character line ("stroke width" in typography) per frame. Otherwise, the human eye will see a gap between the location of the text character strokes on each frame. and this will appear as a stroboscopic effect. This is why I'm credit rolls it's better to use sans-serif fonts that have large stroke width - at least the strokes that are perpendicular to the on-screen motion of the credits.

For example, for a vertical text roll you want to use a font that has healthy horizontal lines - because you'll be limited in far you can move the credits per frame by the width of the horizontal strokes in the credits text. For horizontal scrolling text you need fat verticals in your font. And so on.

Personally I think horizontal scrolls are nicer and more legible than vertical credit rolls. But a truly confident filmmaker might consider using well-designed static text for credits and forgoing this credit roll jazz. 

I keep referring back to this post for the script and decided to expand on it a little:

t = time;
fr = t/thisComp.frameDuration;
x = value[0];
s = 4; //Speed in pixels per frame must be a whole number
inP = timeToFrames(inPoint);
y = value[1] - ((fr-inP) * s);
[x, y]

This starts the scroll on the in point of the layer, so it takes the starting value of the layer at the in point and scrolls from there instead of starting the calculation from frame 0.

Mr Bansaw,

If it's going to be used for broadcast  video, I've always noticed that rendering scrolling text to fields  instead of to frames produces smooth motion. Give that a try.

In addition to Todd's questions and Rick's information, I have more diagnostic questions:

Where are you seeing this: viewing a RAM Preview or viewing the rendered file?

If RAM Previewing, what frame rate do you see in the Info pane?

What's the codec of the rendered file?

What are you using to view the rendered file?

Do you have the rendered file on a single hard drive or a RAID?

It could also be that you just won't be able to get a silky-smooth credit roll if you're working at 23.976 fps -- that's a pretty low frame rate, and what do you need for nice, smooth motion?  A higher frame rate, like 59.94.

Because of the interaction between frame rate and motion it's critical that your title roll move an whole number of pixels per frame. IOW, 1 pixel per frame or 2 pixels per frame, and not 2.64 pixels per frame. Interlaced video add must at an even number of pixels per frame.

This is easily accomplished with an expression. The following will give you speeds that will be smooth. Any other speed will give you a stroboscopic effect where the titles appear to jerk around or thin edges will vary in height.

t = time;
fr = t/thisComp.frameDuration;
x = value [0];
s = 4; //Speed in pixels per frame
[x, fr*s]

You may still experience some juddering if the display's refresh rate isn't the same as the frame rate. Using this expression you can be sure that your credit roll with have accurately placed type.

There may still be issues with retinal retention frame rates and other factors at high scroll speeds. The solution there is to increase the frame rate of your title roll comp, render it, then time remap with frame blending. Perfect rolling titles at high speeds are not a walk in the park. Rolling titles at a speed of up to about 4 pixels per frame are fairly straight forward.

Here's a page with some explanation and tips regarding vertically scrolling text:

"Best practices for creating text and vector graphics for video"

Tell us much more about your computer, software, and composition---as well as excatly what you mean by "jerky".

In general, the more information you give, the better we can help. What version of After Effects? Have you installed the recent updates? What operating system? What kind(s) of source footage? Are you rendering with OpenGL? Does the problem only happen with your final output, or does it happen with RAM preview? Are you using Render Multiple Frames Simultaneously multiprocessing? Are you using fields/interlacing or just progressive?