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Posted: Sat Jun 24, 2017 11:33 am
Seems like I have a blackout, but how can I IVTC a 59.94 telecined 25fps source using DGTelecide() and DGDecimate() such as to get the 25.00 fps progressive source back?
(I think the 59.94 telecined material is 3:2:3:2:2 telecined)
Posted: Sat Jun 24, 2017 12:05 pm
Please post a sample. There are too many uncertainties in your post to comment yet.
Posted: Sat Jun 24, 2017 1:56 pm
Here is a sample (sorry for the confusion, I meant a 25 => 29.97 telecined source, not 59.94)
Posted: Sat Jun 24, 2017 5:41 pm
This script makes the video 25 fps.
dgdecimate(cycle=6,keep=5) # makes 24.975 fps
The stream has no audio, so I could not assess whether the 24.975 vs. 25 will be an issue. Worst case, you may need to shrink the audio a bit, or leave it at 24.975 if your target format accepts that.
Posted: Sun Jun 25, 2017 5:06 am
Thanks! I came to the exactly same conclusion with my experiments, but I thought I might have missed something. So there is no "direct route" for IVTCing this by field matching plus m by n decimation to hit the 25.00fps
Actually, it is not a real problem. I just bumped across it when I converted a 25p (deinterlaced mpeg2 PAL 25i home video) to 29.97i using good old DGPulldown, and encoding it to AVC (x264). When inspecting the hard-telecined alternating 3p-3c-3p-3c ... and 4p-2c-4p-2c... pattern every about 100 frames (p=clear, c=combed frame) I wondered how the heck to IVTC this properly.
Posted: Sun Jun 25, 2017 6:48 am
For your 29.97 fps file of 1524 frames, there is no choice of M and N that exactly gives 25.000 fps. You can get a little closer to it with TDecimate because TDecimate allows a cycle up to the size of the file. For example, this gives 25.014 fps:
The problem really arises because pulldown from 25 to 29.97 cannot exactly hit 29.97 unless the number of frames is very large. As long as you decimate the added fields then assumefps(25) will recreate the original file.
Posted: Sun Jun 25, 2017 10:00 am
Ah I see, very clear. We can't take the total frame number out of the equation. Thank you.
Posted: Sun Jun 25, 2017 10:36 am
You're welcome, Sharc. It's always my pleasure to discuss interesting problems with you.