30fps to 25fps

Apple Final Cut Pro Legacy

30fps to 25fps

Posted by James Mcknight on February 9, 2011 at 10:03 pm

Hi, I’m editing a showreel which will be going out to PAL DVD, so I am editing in a 25fps sequence.
However I have been given some footage at 30fps in H264 compression, with interlacing on every 4th and 5th frames.
What is the best way of converting this to 25fps USING SOFTWARE ONLY.
I have been told the best way is to do a pulldown to 24fps, then to convert that to 25. Can anyone guide me through how best to do this using only FCP / Cinema Tools?

Thanks a lot,

James

Walter Soyka replied 15 years, 2 months ago 3 Members · 10 Replies
10 Replies

Walter Soyka
February 10, 2011 at 2:05 am

[James McKnight] “I have been told the best way is to do a pulldown to 24fps, then to convert that to 25. Can anyone guide me through how best to do this using only FCP / Cinema Tools?”

That’s good advice. The 30fps footage you have now has telecine pulldown, and this must be removed. You can do in Cinema Tools by opening the clip and clicking the Reverse Telecine button, then manually specifying the pulldown cadence.

Like Dave said, though, you really want to use Compressor so that you can transcode your H.264 footage to a more FCP-friendly format like ProRes. Enable Frame Controls and set the Deinterlace option to Reverse Telecine. This will automatically detect the cadence.

Regardless of which method you use to remove the pulldown, you’ll end up with a 23.976 or 24.0 fps movie. Open this in Cinema Tools, click the Conform button, and choose 25.0 fps. This will speed up the movie about 4%, so the run length will be slightly shorter and the pitch will shift up slightly, but your video will be all clean progressive frames with no interpolation.

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
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James Mcknight
February 10, 2011 at 2:07 am

Thank you, works a treat.
James Mcknight
February 21, 2011 at 4:26 am

OK, sorry folks. I have returned to this footage after a while and it now appears to me the above method has not been as successful as I first thought (unless I have missed a crucial step somewhere). The Reverse Telecine in Compressor does of course remove the interlacing, which is great, but it seems to be at the cost of dropping one frame every four frames. Have I done something wrong?

Thanks,

James
Paul james Gomes
July 8, 2011 at 10:02 pm

Hi, I’m a film student at the Edinburgh College of Art, and I’m editing a documentary at the moment. Part of my footage is shoot in hdv 1080i50 PAL (25fps, 1440X1080) and part of my footage is from Nikon S8000 still camera hd NTSC (29.97fps, 1280X720). my final output will have to be in hdv 1080i50 PAL at 25fps.
I did the following:
First of all I converted all the Nikon footages to apple prores 422 through MPEG Streamclip (keeping the frame rate at 29.97). then made a quick time movie in the FCP. after that I only took the video and changed the frame rate 29.97 to 25 in the cinema tools (leaving the Audio untouched). Which is now longer then it’s supposed to be.
then I created a new sequence (with easy setup: HDV 1080i50) in FCP and paste the original sound clip and noted the duration of the clip on this sequence.
Then I opened the video (which is now longer in duration, because of the frame rate change) in Compressor changed it to HDV1080i50 and in the frame control option, I changed the duration of the clip to the length of the audio. After the compression I pasted the video on the HDV 1080i50 sequence on top of the audio.

But the audio doesn’t seems to be an perfect match. I have noticed that, when I paste the Audio from a 30fps NTSC sequence to the PAL hdv 1080i50, the length of the audio gets squeezed. I’m going wild with this project. I need to submit the film on 29th July. Can you please suggest me, what the best way to handle this project?
Walter Soyka
July 11, 2011 at 3:30 pm

Paul, I wouldn’t recommend the workflow you’ve tried. Here are a couple other options:

If you want to slow the footage down from 29.97 to 25 (conform), do it in Cinema Tools and let the audio ride with it. You can adjust the pitch back up later if necessary with an audio effect.

If you want to keep the length of the footage the same, but change the frame rate from 29.97 to 25 (conversion), bring the 29.97 fps clips into Compressor and drop a 25 fps preset onto them. Enable Frame Controls, and choose either Better or Best for the Rate Conversion.

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
Paul james Gomes
July 11, 2011 at 5:45 pm

Hi Walter, Thank you so much for your reply. I want to keep the duration same. I tried something similar to what you suggested. I put hvd1080i50 preset to the 29.97 footage (converted to Apple ProRes 422 with MPEG Stream Clip), and let the audio pass through. it was ok, but the audio is seems sometimes not sync. What I didn’t do is enable the frame control (as I thought the preset is doing that and also if I clicked the option ‘so the source plays at 25fps’, it changed the duration of the clip. I’ll do as you have suggested. I have some request, can you please explain what actually the frame control does here? Secondly, should I pass through the audio or not. And lastly, Should I put the 29.97 H.264 footage directly to the compressor. or convert them to Apple ProRes 422 before putting it to the compressor? Sorry to bother you with all these naive question. But it’s a great help for me. Thank you again.
Paul
Walter Soyka
July 11, 2011 at 6:46 pm

If you’re editing in FCP, I’d use ProRes for editorial.

Clicking the option “so source plays at 25 fps” tells Compressor to interpret your initial file at 25 fps, not 29.97 fps. It keeps the same total number of frames, but makes the duration of each frame a little bit longer, altering your total run time.

To keep the total duration the same, you actually need the computer to synthesize new frames at the new rate based on the original media. See the math below for why.

Enabling Frame Controls allows you to control how Compressor handles resizing, interlacing, and frame rate changes.

A 25fps frame is 1/25, or 0.04, seconds long. A 29.97fps frame is 1/29.97, or approximately 0.0333667, seconds long. As you see, they don’t line up. Frame 1 at 29.97fps refers to a point in time (0.033s) which occurs slightly before Frame 1 at 25fps (0.04s). To do a standards conversion, the software has to guess at what the image would have looked like during the gaps in between frames of the original footage. See the attached table which relates whole frames at 29.97 fps to fractional frames at 25fps.

When Compressor is set for Better or Best rate conversion, it actually analyzes the motion of each pixel in each frame of video over time. This lets it build a mathematical model that smoothly connects pixels from one frame to the next, called optical flow or motion estimation. Once the application knows the real position of each pixel at specific points in time (the original footage) as well as its estimated motion vector in between those points (optical flow), it can more accurately predict the position of each pixel at arbitrary points in time. This lets Compressor synthesize all new frames at 25 fps from the 29.97 source.

WHOLE FRAMES AT 29.97fps >>> PARTIAL FRAMES AT 25FPS
0 0
1 0.834167501
2 1.668335002
3 2.502502503
4 3.336670003
5 4.170837504
6 5.005005005
7 5.839172506
8 6.673340007
9 7.507507508
10 8.341675008
11 9.175842509
12 10.01001001
13 10.84417751
14 11.67834501
15 12.51251251
16 13.34668001
17 14.18084751
18 15.01501502
19 15.84918252
20 16.68335002
21 17.51751752
22 18.35168502
23 19.18585252
24 20.02002002
25 20.85418752
26 21.68835502
27 22.52252252
28 23.35669002
29 24.19085752
30 25.02502503

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
Walter Soyka
July 11, 2011 at 7:07 pm

Replying to myself…

Though the table I showed you is correct and still illustrates the concepts behind frame rate conversion, it wasn’t the right one for your conversion to 25fps.

The table below illustrates the 29.97fps to 25fps conversion.

WHOLE FRAMES AT 25fps >>> PARTIAL FRAMES AT 29.97fps
0 0
1 1.1988
2 2.3976
3 3.5964
4 4.7952
5 5.994
6 7.1928
7 8.3916
8 9.5904
9 10.7892
10 11.988
11 13.1868
12 14.3856
13 15.5844
14 16.7832
15 17.982
16 19.1808
17 20.3796
18 21.5784
19 22.7772
20 23.976
21 25.1748
22 26.3736
23 27.5724
24 28.7712
25 29.97

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
Paul james Gomes
July 12, 2011 at 1:04 am

but should I pass through the audio or not? Thank you Walter. you are great.
Walter Soyka
July 12, 2011 at 1:20 am

[Paul James Gomes] “but should I pass through the audio or not?”

I would — but since you’re using rate conversion, the duration shouldn’t change, so it shouldn’t matter.

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

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