25fps - 24fps - Help!

[paulspurrier]

I'm sure I am not the first person to get confused by the framerate business, of dealing with video and audio at one frame rate that was created in another, and will be viewed in another.

I am terrified that somehow everything is going to go horribly out of sync!

This is my project. I have a theory, but it would be good to get confirmation of it.


This is a film project. It was shot at 25fps. It was telecined at 25fps. It has been edited at 25fps. The timecode on the DATs is 25fps. The sound EDLs from the edit are 25fps.

At least it's consistent.

But...

Since it is a film project, it will be shown in cinemas at 24fps.

I have to construct a plan for the audio post-production, and work out at what stage the material all gets slowed down.

In the old analog days, I did this once, and kept it 25fps all the way to the print, and just relied on the projector to do the slowing down. Theoretically everything was reduced in pitch slightly but since it was consistent it wasn't noticeable. However with digital soundtracks, I think that could be disastrous.


My first task is to give a copy of the film to the music arranger.

I do not want to give him a 25fps copy. If he composes music at 25fps, it is unavoidable that at some stage, the music will have to be slowed down to 24fps. I know that digital conversions, frame rate and samplerate converters do a good job these days, but it seems to make no sense to do this. Why not get him to do the music at the correct speed?

So my plan is to take the current 25fps video and convert it to 24fps. In the process I will effectively be slowing the playout by 4% i.e. making the total timelength of the file 4% longer, so that I produce a video file that is true 24fps, and where it is a frame-for-frame conversion.

Obviously such a file could not be recorded onto a conventional tape, or played through a TV, as it would be a 'real' 24fps file. However, it is my theory that if I output as a quicktime or other file, and send as a data file rather than a PAL or NTSC file, it should load into ProTools or whatever he uses.

He can then work at 24fps.

We then have to autoconform the dialogue and add sound effects. I propose that a project is set up at 25fps, and the dialogue is autoconformed.

But then, I would want to convert that project to 24fps, before adding sound effects, and adding the music. In the process, all the conformed dialogue would need to be sample-rate converted, so that it plays 4% slower, and lasts 4% longer.

Is this possible, and how would one do it?

And how would one supply video as a guide for ProTools?
Can ProTools play a 25ps video file back at 24fps?
Or would I have to create two QuickTime files - both with the same number of frames, but one set to play at 25fps and one set to play at 24fps.?

I would be grateful for any confirmation that this route is all possible.

Thanks.

Paul

[Branko]

Paul,
the biggest problem in your approach would be the production sound - if you "slow down" the picture to 24 fps, you'll need to slow down the dialogue too, in order to keep the sync. When you receive the picture from your film editor, the production sound will be chopped in hundreds of pieces all over the timeline. How can you slow these down and still be able to edit? Not impossible, but painfully slow and expensive.
This is the main reason to keep the project at 25fps till the very end, then slow down final stems and harmonize them to mantain the correct pitch. Doing so will help you to produce the M&E easier. Music will play at the correct pitch, voices won't suffer, but everything will be slower, including the picture. But, that's something that's accounted for from the very beginning of the project, when the decision to shoot 25fps was taken.
Good luck
Branko