Not seen any specific data, but the way I see it....

A) It's easier to remove frames than add them I'm

B) Over half of my sales come from the US and they use 30fps, so it makes sense for me to go with that.

I could be wrong, maybe people are crying out for 24fps. Obviously if the majority of your buyers are from the UK then it would make sense to go for 25fps... but I still think it's better to have more frames to be on the safe side.... I mean, the UK buyers might be creating content for US clients!

Not to.mention that the Internet (where I'm guessing most of my content is used) is pretty much 'non-framerate-specific', so I don't think you should worry about it too much.

4K 60p is best

I'm no expert in the software you speak, of but if you need six extra frames then they've got to come from somewhere... so you're either going to have duplicate frames, or interpolated frames... which will probably do the job but can be noticeable. Unless I'm missing something, I'm not sure how it could be done flawlessly.

I'm no expert in the software you speak, of but if you need six extra frames then they've got to come from somewhere... so you're either going to have duplicate frames, or interpolated frames...

Why? I would expect that the conversion process just changes the duration of each frame, for example from 1/30 s to 1/24 s, or vice versa. But I am not sure, I have never done it.

As long as the agencies accept all common frame rates or don't have a preference, I don't really care much.

Well you can convert to 24 from 30 by dropping the occasional frame here and there. But to go from 24 to 30 you need to find six extra frames from somewhere. You could alter the duration of each frame to fit, but then it's still only 24 frames as there's only 24 individual still images to make up that second. I can't think of any physical way that you can increase the frame count without using duplicated frames or some kind of frame blending/interpolation.

Fortunately most of our work has no audio associated with it so rather than add or subtract frames it often makes more sense to retime the clip. I think PP calls it conform footage and FCPX is Automatic Speed. 24fps to 30 looks a little faster while 30 to 24 is slightly slomo. I personally find slomo more pleasing. It may not work with all footage but for a lot of it you simply don't notice any difference. 24p has more jutter and is widely accepted but it also has more rolling shutter and jello issues depending on camera, not so good.

I can't think of any physical way that you can increase the frame count without using duplicated frames or some kind of frame blending/interpolation.

Yes, this is what's called a 3:2 pulldown and it's used for every film you see on TV in the US. They are all filmed at 24 frames per second but when viewed on television they blend in 6 extra frames to make it 29.97. Most high-end commercials are also filmed at 24 frames per second (or 23.976) but displayed as 29.97 when showed on TV.

The same films when shown on a PAL (25) system will usually be sped up 4% along with the audio (the audio will retain its original pitch however).

If you convert 29.97 to 23.98 or 25 by just removing frames you will get a stutter effect which may or may not look too pleasing. We are, however, very used to seeing 24 frames pulled down to 29.97 because it's how films have been displayed for so long.

Anyway, I have yet to decipher what sells the most as all frame rates seem to do well. Of course, there are more 29.97 clips out there because of all the American producers with NTSC cameras so in total, 29.97 has more sales. But perhaps not per clip.

I have read countless forums on this very topic, and I still haven't found a clear answer to what sells best in the stock footage world. Some of the world's top producers use 23.976, some use 25, and others use 29.97. Just check the P5 bestsellers. VIAFilms and AILA are mostly 23.976.

Yes, in the submission guidelines they say that any progressive frame rate will be converted to 23.98p.

I often film in 29.97p with a 1/50th shutter and then slow it down to 80% and deliver 23.976p. It's a decent way to get dreamy looking 4k footage with a camera that can't shoot 4k60p.

I think it really only matters with footage of people that's supposed to be in real time. That's when we would notice that something might be off if the speed changes.

Any timelapse or slow motion footage could easily be slowed down or sped up to fit another frame rate without looking or feeling strange at all since it's not real time anyway.

Shoot 24 / 23.976.

Plus, by shooing 6 fewer frames per second gives each frame about 20% more bandwidth (when shooting at a constant bit rate).

I agree with you, and I do 90% 23.976, but this statement doesn't automatically mean better quality. Only if you're using intra-frame codecs (like ProRes). If you're shooting in the more common h264 (inter-frame codec) there will be more movement between each frame in 24p, and since inter-frame codecs compare frames that 20% extra bitrate could just about make up for the increased change from the previous frame. Or in the case of very fast movements, decrease the quality.

For aerials, for example, it can make sense to film in 29.97p since everything in the frame is moving constantly.

Nitpicking here, but just to be clear.