Many are confused because of the marketing ploy that somehow recording only 24 fps instead of the video standard 30 fps will transform the look of video to look like film.
But frame rate has nothing to do with the look. Just pause a football game on your DVR. Does it suddenly look "film like?" No. It just looks like frozen video. Do the same for a movie and it still looks film like.
That's because the film look does not lie in frame rates. iMax used 48fps in some theaters in the 1990's and I thought it was very film like. RED digital movie cameras simulate film looks very well but their 30 fps gallery samples look just as film like as the 24 fps ones. The film look lies in things like the gamma of film and the boundaries between contrasting regions of an image. In video with high "presence" there is a distinct boundary, and a hard cut, or hard transition between highly contrasting regions of an image, such as a yellow sail against a blue sky. It's almost as if a thin black line separated the two. The sail "pops" against the blue sky more like real life.
In the awful "motion smoothing" gimmick that is being added to 120 and 240 Hz LCD TV's they actually do add a thin black line around some images, making a movie look like it was a behind-the-scenes Handycam shot. Awful! In fact, in Best Buy the other day they were playing a Green Hornet promo as part of the demo video and you literally couldn't tell the actual movie scenes from cheap behind-the-scenes shots except one had cameras and crew and the other didn't. Great! Turn multi-million dollar movies into junk that looks like it was shot on a $400 Sony.
But film, and the high end "digital cinema" video (Panavion and RED) have softer transitions than video and look exactly like film except without grain or jitter--two artifacts film makers try to eliminate.
That's because film has a much greater dynamic range that older video. What that means is a "softer" look. If you've played with HDR (high dynamic range) digital photos you know what an unprocessed HDR photo looks like: flat, low contrast, sort of grayed out like it was foggy when you took the photo. That's because you've captured a lot of dynamic range (a lot of shades of gray if you will) between the brightest whites and the darkest blacks. Film stock doesn't go to that extreme, but it does capture more dynamic range of luminance than older or low end video, blending contrasting regions more gently.
Actually the "p" part of 24p does help somewhat. Progressive video does not have the "feathering" artifact of old NTSC interleaved fields. Go back and look at some home video from the 90's or early 2000's that you've uploaded to your computer (assuming you have an LCD display) and you'll see when motion occurs there is a jagged edge, or "feathered" edge where the odd and even fields of video interleaved 60 times a second. Progressive video (both SD and HD) removes that artifact. In QuickTime you can deinterlace old video and on an LCD display it does make it look more film like, simply because it removes obvious artifacts.
Film has some interesting advantages related to it's look:
Ironically film masks the use of painted props because it does not pick up subtle clues that video does. If you've ever seen a set on a "behind the scenes" video it all looks fake. You can tell it's plywood and plastic and not brick and steel. That means that within the film world everything looks more plausible, more real in a sense. Film makers have long known this and that's why live staged sit coms like Cheers were shot on 16 or 35 mm film even though they were going to be shown on TV. The 2nd Bob Newhart show actually begin in video for its first few episodes, and it looked obviously fake. The producers quickly switched to film and then the set looked like a real Vermont hotel. It was believable.
Further proof that 24p does not magically transform video to film like are all those awful local cheap TV commercials being shot on Handycams at "film like 24 p" but jump 6 frames every second to make up for the fact they are missing 6 frames! What editing software are these clowns using? I can't even make Final Cut do that. But the point is their funky video for local merchants looks like video. Bad video at that.
Why 24fps in film, then? Because it's cheaper than 30 or 48 or 60 fps. Animators, whether traditional or digital, do not want to have to deal with more frames per second. Shows and movies shot on real film ditto. And even digital cinema camera usually stick to 24p because 1) it takes less storage and 2) they can get away with it and 3) most of the industry is geared that way.
But you can take a digital cinema camera and shoot 30fps and it still looks very film like. Or, take the Nikon D7000 and shoot 720p and 30 frames per second with a wide aperture and you'll see it is very film like, despite being shot at a "video" rate.
The only film-like thing 24p does is make some motion, particularly panning, look a little less smooth. But suppose you had a scene of a speaker standing at a podium waiting to begin speaking, almost motionless. You could instantly distinguish low end HD video of that person versus had it been captured on 35mm film. It just looks different, even when frame rate is not affecting motion.
But the line is blurring! I mentioned the Nikon D7000 SLR. You can watch video samples on YouTube where a wide aperture throws the background into soft focus and you will think it is film, despite being captured in 30fps. And the Red camera has become a mid-range digital "film" staple that perfectly mimics the film gamma and transitions between contrasting regions. But, a still frame from the Red will look film like because of how it handles image information, not frame rate. Of course many films today are being shot on high end digital film cameras such as Panavision or Arri as well. But it's all image handling, not frame rate that really makes the "film look."
Conversely, sports and news are two media that despite using high end HD cameras intentionally dial up contrasty, punchy video to give a more live "you are there" look.