Jerky rolling credits -- how can I solve?

Here's a step by step method for creating a perfect credit roll every time in less than 5 minutes using a text layer. You can use the same technique using Illustrator or Photoshop to create your text but a text layer is easier.

1. Choose a sans serif font because the thin lines in a serif fonts cause problems in video unless the fonts are very large
2. Press Shift + Alt/Option + Ctrl/Cmnd = t to add a new text layer
3. Copy and paste your credit roll text from a text document to the new text layer
4. Make Set the paragraph style and font size to something that looks good
5. Set you Comp Panel Magnification Ratio (first box on the bottom right comp of the Comp Panel) to 800% or 1600% and the Comp Panel resolution to Auto so you can clearly see the top and bottom edge of your text
   
6. Here comes the first important part. If you insist on using white for your font color and a dark background then bring down the white value to something below 220 or compression will foul everything up with compression artifacts when you render
7. Carefully check the top and bottom edges of your text. In this case there is some sub pixel sampling fouling up the top edge of the "T"
8. Hold down the Ctrl/Cmnd key and drag the font size slowly up or down to minimize the aliasing on the top and bottom edge of your font. If the baseline is set to zero you should not have to adjust the baseline. Then adjust the leading so that each new line has the same look and aliasing is minimized.
   (NOTE: Holding down the Ctrl/Cmnd key lets you drag values in the comp panel with 10 times the precision as just dragging them. If you are using Photoshop or Illustrator files for your font size you can make these adjustments in either app by zooming in. If you are in Illustrator you must have pixel preview turned on to see the aliasing problems and fix them. If someone else prepared the files you can use the "y" scale to line up the edges and set the starting Y position.)
   
9. Now you have the text lined up with the pixel grid so that it looks as clear as you can make it look. Change the Composition Panel's Magnification Ratio back to 100% or 50% so you can see the entire composition. DO NOT use Fit because Magnification Ratios like 45% will foul up the preview and make you needlessly worry about the credit roll.
10. Add this expression to the Position Property of your text layer by holding down the Alt/Option key and clicking on the Position stopwatch. You can copy and paste from this post:
    

    s = 3; // speed

    y = value[1] - time/thisComp.frameDuration * s;

    x = value[0];

    [x, y]

11. Grab the Text Layer and move the text to the bottom of the frame making sure that you don't position the Y value on a half pixel and foul up the top and bottom edges of your text
12. Turn on Motion Blur for the text layer and the comp, make sure the shutter angle for the comp is set to at least 180º and the phase is -90º (generally phase should be -half the shutter angle). Preview and check the speed. If you want the credits to move faster change the "s" value to 4 or 5. Use whole numbers. Some speeds may give you stroboscopic effects which are worse at lower frame rates. If you are rendering interlaced video then the speed should be even numbers. Your preview may stutter a bit in the comp panel because of screen refresh rates and frame rates or AE's current preview/cache problems but if you are paranoid you can check the comp a frame at a time. Comp frame rates of 29.97 will produce smoother looking credit rolls than 24, 23.976 or even 25(pal). If you use 24P as your format you must realize that broadcasters in NTSC land will add a synthesized 3:2 pulldown to your video and the credit roll will have funky aliased edges every third frame where two fields are combined to make one frame.

Let me explain the expression line by line. The first line declares a speed variable that defines the number of pixels the layer will move per frame. The second line defines the "y" value for position by taking the original value for y and subtracting time divided by the duration of a single frame then multiplying that value by the speed variable. The next line just calls up the "x" value for the layer. The last line puts the defined "x" and "y" values in an array that can be used to position the layer.

One other thing. If you need to change the timing of your credit roll and it will not fit using a whole number for "s" then you change the leading in the text layer so the lines are closer together or farther apart. Make sure that you go back to a Magnification Ratio of about 800% and check the top and bottom edges of your text.

That's all there is to it. To save yourself time in the future select the position property of the text layer and save this animation as an animation preset. There already are two presets that kind of do the same thing but they tile the movement. They are Autoscroll horizontal and vertical. I prefer my method because the Autoscroll presets repeat the roll as a loop and most of the time I don't want that.

I suppose I left out a critical element: time.

"You've got a minute on the button for the credit roll."

"Yeah, but the roll doesn't look good unless it's at a minute-ten."

"Fix it."

That's when it becomes a pain in the neck.