Any reasons why this might be a bad idea?

Hello everyone, I had a recent realization that I'd like to discuss. There have been numerous discussions about using 60fps footage in a 24fps timeline. It occurred to me, why not shoot at 60fps and place it directly in a 60fps timeline? If I need to create slow-motion effects, I can simply slow it down to 24fps (40%) and still achieve smooth slo-mo. I conducted an experiment to test this approach, and I must say, the results turned out just fine! I'm currently adhering to the 180° shutter rule, so my footage maintains decent motion blur. Can anyone think of any reasons why this might be a bad idea? I'd love to hear your thoughts.

It seems perfectly logical to me and is the method I have always used.

EDIT: I have thought about it a bit more and realised that I shoot 50fps (PAL) and only ever use either 50fps or 25fps projects so simply using half-speed slo-mo in my case does not result in any additional fake frames.
In your situation the speeds are not multiples so fake frames will be created which in theory will produce video that is not quite as smooth. Whether this is noticeable can only be checked by testing both ways to see which, if either looks better.
I do not use 24fps as I consider it a fad. It had to be used in the old film industry simply because film stock was so darned expensive and took up so much space. If acetate had been cheap they would have shot at 30fps or 60fps and achieved smoother, more natural motion but they couldn't because of cost and physical bulk.
Now we can shoot at any speed with no thought to expense or bulk and have lenses etc. that can produce exceptional results but some people yearn for the crappy jittery look of film.
Why not go the whole hog and return to cave paintings . . . ?

If you shoot at 60, put it in a 60 timeline, then slowing the footage will result in duplicate frames. This will look juddery compared to the full-speed footage.

If you shoot at 60 and put it in a 30 timeline, slowing your footage by 50% will result in nice smooth slow-moving footage, and you're using all of the frames you shot with no duplicates.

It really depends on the look you're going for. Me? I like my moving shots to be smooth as silk, and it drives me NUTS to see janky pans in 'professional' productions. Happens all the time, nobody seems to mind..

2¢

If you select "Optical Flow" instead of "Standard" as your Video Quality when retiming you will get silky smooth action.

SeanJackson wrote:

...There have been numerous discussions about using 60fps footage in a 24fps timeline. It occurred to me, why not shoot at 60fps and place it directly in a 60fps timeline?...

The simple answer is you can do that. In fact it's often best to shoot at the final delivery frame rate.

However you may be thinking about a small, single-user video project, and may not be considering delivery criteria requirements. For a project shot and edited by one person, you can mostly do whatever you want. If there are multiple camera operators (whether concurrent or over time) they should coordinate the shooting frame rate with each other and with the final distribution frame rate. 

Another issue on larger productions is that 60 fps takes a lot more data than 24 fps. It's less an issue on a short single-camera production using an H264 or HEVC interframe codec. However a multi-camera production that shoots 60 fps "just in case" slow motion might possibly be needed on a few shots will be burning through a lot of data, especially if using an All-Intra codec.

You can put 60 fps in a 24 fps timeline and using optical flow rate conforming, but that does not always work perfectly and entails a significant computational burden on a large timeline. Each rate-conformed shot must be closely evaluated to ensure there are no morphing artifacts. Shooting 60 fps for a 60 fps timeline avoids that but incurs other costs.

In short, there is no simple answer for this. On some shots there is obviously a need for 60 fps to give the option for better slow motion. If it's a music video, you might shoot everything at 60 fps or even 120 fps. However for a documentary with multicam interviews or a scripted narrative, you may not want 60 fps on everything.

joema wrote:

SeanJackson wrote:

However for a documentary with multicam interviews or a scripted narrative, you may not want 60 fps on everything.

I for one would be interested in the justification of 60 fps and its corresponding heavy data penalty for an interview where the greatest motion to be encountered would be the turning of a head. Roll 24 on these and you should be fine.