Also keep in mind that higher frame rates, without further camera handling technique or processing technique, NORMALLY result in slow motion video when played back at normal speed (your output frame rate is always going to be 24 or 30 frames per second. The high frame rates on TVs, like 60fps, 120fps, etc. are artificial, produced within the TV hardware that does additional inter-frame processing to blend two separate source frames into four or six output frames.) Your video does not play back at 60fps if you recorded it at 60fps...it still plays back at 30fps. So don't think of 60fps as the solution to your problems...ultimately, shooting at 60 or 120 fps just means your creating a slow motion sequence. This is especially true if you are interested in shooting at mixed frame rates, and producing a video that contains normal rate and slow motion sequences...you have no choice but to use the same output frame rate...anything shot slower than that will speed up, anything shot faster than that will slow down.
Ummm.......that is not true. Most modern TVs will handle at least 60 fps, after all, that is what computers put out, and all of them can be used as computer monitors. My TV can handle frame rates up to 240 fps, if it does get that, THEN it interpolates frames. It automatically matches frame rate to the source, and if you have the feature turned on, it interpolates frames to make up the 240 fps if your source does not go that high.
Typical sources would be BluRay or AVCHD output (which may be either 30p or 60p), or a computer (usually 60p)
Just because your typical movie is 24 fps does not mean that all other video is treated the same way.
There is refresh rate, and there is progressive video output. There is also the interpolated motion rates, such as Samsung's CMR (Clear Motion Rate). There ARE some high end premium HDTV channels (i.e. ESPN) that offer 60p progressive frame rates, however for the most part, the majority of HDTV is 30p. My Samsung non-3D TV has a 120Hz "refresh rate", supports 60p output, but as I've never paid for premium HDTV channels (they are extremely expensive, as they use up a hell of a lot of bandwidth), I've only ever seen 30p content on it.
The modern 240Hz refresh rates for TVs were originally created to support interpolated motion rates for 3D video up to 120Hz per eye, or 240Hz in total. BluRay video frame rate
is still 24fps as far as I know, and the supported BluRay playback rates (according to the current BluRay standards) are either 720p @ 60Hz progressive, or 1080p @ 30Hz progressive or 50/60Hz interlaced. The higher refresh rates on TVs avoid timing issues between the video rate and the playback rate (the refresh rate)...i.e. if you had a 24fps video on a 24hz screen, you have to get the timing exact to ensure that each frame is ready to play exactly every 1/24th of a second...if your timing is off (there is always noise, so it's likely), then you end up rerendering the same frame for another 1/24th of a second, causing stutter. With higher refresh rates, timing becomes less and less of an issue. At 60hz, you play back ~0.4 frames per refresh cycle, at 120Hz you play back ~0.2, and at 240Hz you play back ~0.1. You still can't get timing 100% exact, which is where interpolation like CMR comes into play, which smooths things out if you end up having to re-render the same frame for an extra refresh cycle.
The key is to note that even though BluRay and HDTV channels support playback (officially) at 30p or 60i (or even 60p, as in the case of some premium HDTV channels), the VIDEO ITSELF is still usually
filmed at 24fps for standard motion. I am also quite certain that even the 1080p @ 60hz channels are still filmed at 24fps (I think if they were filmed at 60fps, people would have started complaining about it like they have with The Hobbit, and I've not read about any such thing.) Filming rate and playback rate are very different things. Filming rates, for standard motion, higher than 24fps are still VERY new, and not many productions have used those frame rates yet. If you want fast motion, you would have to film at lower than 24fps (or do timelapse), and if you want slow motion you would have to film at higher than 24fps. This is IRRESPECTIVE of the playback rate, whether it is interlaced or not, etc.
Regarding Don's problem with a beat frequency in bird wings, if you have software capable of doing it, you could probably record at 60fps, then interpolate that sequence back down to 24fps for inclusion with other 24fps sequences, WITHOUT resulting in the 60fps sequences playing back as "slow motion". I'm not sure if something like Adobe Premier can do that, or whether you would need higher end software. Either way, there isn't any mixing and matching frame rates in a single final output video. If you record at different frame rates, you either string them together in a tool like Premier, and anything filmed faster than your output rate ends up "slow motion", and anything filmed slower than your output rate ends up "high speed motion".