Let me put it this way, the lower the frame rate the more difficult it is to avoid problems when things move in the frame. Film in the United States is traditionally shot at 24 frames per second but a film projector as a butterfly shutter that runs twice that fast so you actually see every frame twice. This makes the human brain B believe that the light is not flickering. I know that sounds confusing but it isn't really. When you sat in a movie theater and projectors still ran film you saw 28 pairs of 24 frames per second. Are you following this?
Let me explain further. In a motion pictures theater 24 slices of time were shown to your brain 28 times a second. This solves the light flickering problem and gives you a different amount of motion blur in the action on the screen than you would get if the film was shot at 30 or 29 or even 28 frames per second.
Have you ever noticed when watching a western that sometimes stagecoach wheels turn backwards? This is caused by the stroboscopic effect that happens when the speed of the wheels interacts with the frame rate. This same problem can also happen with horizontal or vertical detail as the camera pans or tilts or a person walks through a shot. When horizontal or vertical and detail does not move smoothly because of the speed versus frame rate problem we call that "judder" and it's horrible on the eyes. A good cinematographer carried with him or memorized a critical panning speed chart to avoid these kinds of problems. Critical panning speed problems at 24 frames per second are much more pronounced than they are at 29.97 which is basically 30 frames per second. (Note: 29.97 was a frame rate required to make color television work when the technology was invented because 30 frames per second black-and-white video had to be slowed down to make time for the color information to be broadcast).
One more scientific fact before we move onto my recommendation. Computer monitors also flash on and off but they do so at a refresh rate (frame rate) that is usually 50 or 60 times per second at least. If your computers refresh rate was 24 you could not stand to look at it.
In Europe the frame rate for motion picture film and tv is 25 fps because their electricity runs at 50 cycles per second. Ours runs at 60 and only an American would try to divide 60 by 2.5 to end up with 24. We do everything the hard way.
So here is the recommendation. To minimize potential problems with critical planning speeds use the US standard 29.97 fps as your standard frame rate. This will allow you to use standard video in your projects with no problems. If you want to experiment with 24 FPS video, which is really 23.976, then make sure that you understand and take into account the limitstions and you have to be much more careful with the motion in your shot, when panning the camera, or adding graphics that move do your project or you will be back on the forum asking us why you don't have smooth motion in your video. Making video is both science and art and if you don't follow the rules of the science you can't make the "art" work the way you want it to.
You will find those who say that if you want video to look like film you must shoot at 24. I personally do not believe that to be true at all. Most of the film that I have shot on 35 mm film for national and local high end agency commercials during my 40 plus years in television were shot with the film camera running at 29.97 frames per second because they just looked better than shooting at 24 and transferring to video.
One last word, there are a lot of folks wanting to shoot and produce at 59.94 or "60" and that's OK. Video streaming services are supporting these higher frame rates but in most cases most people will end up seeing only every other frame as the video is playback on their computer screens.
One last cautionary note. Make sure that your composition frame rate matches the frame rate of the video you're including in the project or that the frame rate of the composition is exactly half of the frame rate of the video. Cell phones and some consumer cameras may give you some very odd little frame rates like 28.135. If you see something like this from consumer video in the info panel then reinterpret the footage to the nearest standard frame rate. If you have high frame rate footage that you want to use as slow-motion footage in your project reinterpret the HF are footage to match the frame right of your composition.
That should about do it. Probably more than you wanted to know and I should probably write an article.
Thanks for the thorough explanation, Rick! This was a helpful read. The footage I was working with seemed to be NTSC 29.97 fps, so I ended up using that to match. Main concern was whether compatibility was a concern anymore, for videos whose destination is the web. Thanks!
If the destination is the web, technically it doesn't matter. However, you certainly want your AE comp to match the frame rate of your footage (and, as Rick says, sticking with standard frame rates is wise). Going off all willy nilly is just silly. Now, for artistic purposes, some people do weird things, but you have to know the rules before you can break them.
Do what Rick suggests. And, Rick Gerard, you should definitely write an article. Your post, with only minor changes, would be excellent!
The easiest way to match your composition to your footage is to simply drag your footage onto the New Comp button in the project panel. It will create a composition that matches the dimensions, frame rate, and length of your video clip. It's easy enough to change the composition time if you want it to be a different length, but this is the quickest and easiest way to match all of the other technical specs of your video clip.