Exporting 240fps iPhone footage in the same format as original

Because I have a camera that can shoot 60fps, I will use 60fps as an example. Results of this explanation will hold true for other frame rates like 120 or 240, simply adjust math accordingly.

If I shoot 60p video and drop that into a 60p sequence in Premiere, the frame rates match and Premiere plays every frame of video in real time, just as it was recorded.

If I drop that same 60p clip into a 30p sequence, Premiere assumes that I want to view it in real time - no slow motion - and so it plays only every other frame to compensate, the result being that the clip playback looks to the viewer as if it was shot at 30p. Happens in the background without user intervention. If a 120p clip is dropped into that same 30p timeline (and that clip is flagged internally as being 120p), that clip should also play real time in the 30p sequence (Premiere only displaying every fourth frame and skipping the other three in between) to show the viewer 30 frames per second without changing playback speed.

Here's where it gets interesting. Back to the 60p clip in 30p sequence. There are TWO ways to get slow motion from that 60p clip. One way is to simply change the speed in timeline to 50% using Speed/Duration tool. One second of footage becomes two seconds on the timeline. The original clip contains 60 frames per second, and we are only playing back 30 per second, so with 50% speed applied, we can now see every frame played back, none skipped, none duplicated. The result is of course slow-motion video.

If I put a 120p clip into the 30p timeline and wanted to play back every single frame, then I would use 25% speed for playback, and Premiere would be playing every frame, at 30fps. Playback duration would be 4x original, one second becomes 4 seconds. 240p in 30p timeline would  be 12.5% speed to see all frames (1/8th speed).

So that's one way to achieve slow motion. The other way would be to right-click a clip in the Project Bin, before moving the clip to the timeline. Select Modify > Interpret Footage. The panel that pops up allows the user to tell Premiere basically, "Forget what the clip itself reports as frame rate or pixel aspect ratio or field settings, and use THESE settings that I am specifying here".

So - I have a 60p clip (59.94fps) and I modify the frame rate to 29.97fps. I'm rounding numbers here, but because each second of source clip has 60 frames in it, and I am telling Premiere to treat the video as if the clip's frame rate is really 30fps, the duration of the clip is suddenly doubled! My Premiere sequence is 30fps, and the clip is 60fps but I'm telling Premiere to play the clip at 30 frames per second. Since each second of the original clip actually has 60 frames, playing those 60 frames at 30fps takes two seconds now. Drop this clip into the timeline and it plays at 50% speed - without having applied a speed change effect, the slow motion becomes native to the clip.

Now you've already noticed that you cannot tell Premiere to export at 240fps. If you put the 240fps clip into a 60fps sequence, and Premiere plays it back as 60p (no slow motion), three-quarters of the original frames are not being used. If you export at 60p, those additional frames are then GONE from that clip.

So how can you export the 240p clip and retain ALL of the original frames? Import the clip into Project Bin, and Interpret as 60fps (59.94). The clip length will then become 4x longer. Drop it into 60p timeline, and it will play in slow motion, but you will see every frame. Then export at 60p - same as sequence setting - the exported clip will contain all those frames from original 240fps clip. It's just that the new clip will natively think it is a 60p clip - playing in any player, you will see the 25% slow motion version.

If the original 240fps clip was 10 seconds in duration, the new 60fps clip will have a duration of 40 seconds. You've lost no frames.

So what happens when you give the 60fps clip to dad? He can set the frame rate to 240 using Interpret, and drop that clip into a 60p or 30p sequence and playback speed should then be normal. He could then for instance apply 50% or 25% slow motion to portions of the video and it would use the available extra frames to give smooth results. And when he is done editing, export at 30 or 60fps which are standards for video viewing.

Hope this all makes sense. And keep in mind that 30, 60, and 120 fps are actually 29.97, 59.94, and 119.88 fps respectively, so be careful with that, as camera makers typically round the numbers for marketing convenience but you want to get them exactly right when editing and exporting. My calculator says that 240fps might be 239.76 in reality, but I don't know what exactly the iPhone is doing so double-check that figure.

To recap workflow to hand off footage to Dad, keeping 240 fps intact:

1. Import footage into Premiere, and Interpret to desired frame rate (to match Sequence being used). Clip will lengthen.
2. Move clip to timeline, color correct, then export - again using frame rate to match sequence (clip appears slow motion)
3. Dad imports footage, Interpret back to 240 fps (or whatever original clip was) and edit as 30p or 60p (clip plays normal speed)
4. Export as 30p or 60p for delivery/viewing

Thanks for reading!

Jeff Pulera

Safe Harbor Computers