29,97fps to 25fps (NTSC to PAL)

[pietz]

Hey there,

this is an known topic that has been discussed before, but at one point of solving this problem i just cant follow. This is where i am now (please stop me wherever i go wrong):

there is no "perfect" way of doing this, but there are 2 methods to get "good" results:

1. interpolating frames
2. cutting out frames

i wanna talk about the 2 method. i read that its not a good idea to go directly from ntsc to pal because the program will cut 333 frames out of 2000 frames. its better to cut every 6th frames, so ill get 23,976fps and than speed it up to 25fps. this version will not be as long as my original but on the other hand its hard to notice this small change in playback speed. speeding up the movie is something i can do in virtual dub, but first of all i need to cut out every 6th frame and i just dont know how to do that.

What software (freeware or premiere) can i use for this process and how do i do it?

Thank you for your time.

Greetz Pietz

[qyot27]

It depends on what kind of content you're talking about.

If it's a Hollywood movie, chances are that it's already 23.976fps, and uses pulldown flagging to achieve 29.97.  If you use DGIndex you can tell it to Force Film such content - that way when you give it to AviSynth it recognizes it as 23.976fps to start with.  To check, when you open the file to DGIndex, press F6 and it'll start analyzing the stream.  If it comes says 'Film' (without a percentage or a percentage higher than perhaps 90-95%), then you should be able to Force Film it safely.

If it's anime, most American distribution companies hardcode their telecine, so you should perform inverse telecine to bring it back down to 23.976 anyway.

If it's actually standard television content at 29.97fps, only then will you see jerkiness that wasn't in the original if you cut it down to 23.976.


What you can do to avoid that speedup and length difference when converting to PAL, is to do the inverse telecine or Force Film operation, encode the content as 23.976fps progressive content (no pulldown flagging), and then use DGPulldown to do a custom pulldown that will give you 25fps.  This eliminates the need to mess with audio pitch and framerate.  You do still need to make sure the resolution is a PAL standard, though - so instead of 720x480, it'll need to be 720x576, aspect ratio flags considered as well.

[John S. Gook]

If you cut out every 6th frame, you will get 25 fps, and there will be no need to speed anything up or down. 30 * 5 / 6 = 25. Since you are already using VirtualDub, the "Convert to fps" option under Video -> Frame Rate does what you described.

[pietz]

@qyot27: its actually D5 footage so i believe its 1080p 29.97fps

@John S. Gook: first of all, youre right i did miscalculate the 29.97 to 23.976 thing and what you described was the setting i was looking for, but the problem is i need an output of 25fps EXACTLY and the video i have right now is 30/1.001fps EXACTLY. meaning: i cant enter the EXACT framerate to cut out every 6th frame because that number would be 24.97502497502498....

ok, so let me changee my main question:

how can i convert 1920x1080 progressive video material with 30/1.001 frames per second to 720x405 progressive video with 25 frames per second and get the best possible quality?


thanks for helping me guys

[John S. Gook]

Set the framerate to 30, and then drop every sixth frame.

[qyot27]

The AviSynth script (for 29.97->25):

AVISource("sourcevideo.avi") # replace with actual source filter/source used
AssumeFPS(30000,1000,sync_audio=true).SSRC(48000,fast=false) # I'm assuming that the audio is 48kHz, and stereo.  For multichannel, you may need to do resampling using BeSweet or WaveWizard.
Decimate(6)
Spline64Resize(720,400) # I'm going with mod16 here; modify as necessary if you want
ConvertToRGB32() # standard precaution if you're going to edit this in Premiere, as many NLEs work internally in RGB or other weirdness can pop up on export, etc.

Basically, that speeds it up to 30, which is marginal on the sound and probably inaudible, and then takes out every 6th frame.

[pietz]

damn why didnt i think of this

thank you so much