Frame rate conversions

[Walter Soyka]

[Nina Sargsyan] “I just converted a 25FPS footage to a 23.976/24FPS footage. I did this by interpreting the footage in Premiere pro and sending it over to After effects for color correction. If someone could explain as to why my 25FPS footage was 42 secs and 4 frames, and when I made it 24FPS it became 43 secs and 22 frames. I would understand this if I were making the 25FPS into a 30FPS, but I dont understand why the duration increases as I decrease FPS.”

You’re just thinking about it backwards. Lower frame rates have higher frame durations. By re-interpreting the footage with a lower frame rate, you’re actually increasing the duration of each frame slightly, so it causes an increase in total program length.

Here’s some math, if you’re interested:

25 frames per 1 second = 1/25 = 0.04 seconds per frame
24 frames per 1 second = 1/24 = 0.041667 seconds per frame

As you can see, the duration per frame has increased by ~4.1675% ((0.041667 – 0.04)/0.04)

42:04 @25fps = 42*25 + 4 = 1054 frames
43:22 @24fps = 43*24 + 22 = 1054 frames

1054 frames at 0.04 seconds per frame = 42.16 seconds
1054 frames at ~0.041667 seconds per frame = 43.91667 seconds

4 frames out of 25 = 0.16 seconds
0.16 + 42 = 42.16 seconds

22 frames out of 24 ~ 0.91667 seconds
0.91667 + 43 = 43.91667 seconds

It all adds up.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Gina Sarentino]

Thanks Walter for the reply I have been looking for this math all over the internet and couldnt find it anywhere, however, I have one confusion, you said that

42:04 @25fps = 42*25 + 4 = 1054 frames
43:22 @24fps = 43*24 + 22 = 1054 frames

However, in Premiere when I check the Frames in the 25fps footage it shows 1010frames,
and the frames in the 24 it shows 1054 frames.

Why is that the case.

[Walter Soyka]

[Nina Sargsyan] “However, in Premiere when I check the Frames in the 25fps footage it shows 1010frames, and the frames in the 24 it shows 1054 frames.”

That doesn’t make much sense. Can you post a screen shot so I can see what you’re seeing?

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Gina Sarentino]

As I was going to take a screenshot I noticed that I had been looking at a shorter version of the footage and thats why it was showing me 1010 frames. Now that I checked the correct footage both show me 1054 frames. Thanks for the help you helped clear up a lot of my questions.