Pal (25fps) to 23.97fps or 29.97fps???

[tarrickb]

I have PAL (25fps) source xvid movie, and if i want to convert to NTSC, i was just wondering...is it possible (or a good idea) to endoe using 23.97 as the frame rate and apply 3:2 pulldown. Or should i just encode to 29.97???

Please let me know what you think. THANKS!

[sweetfreek]

Bob(height=480)
BicubicResize(720,480)
ConvertFPS(60000, 1001)
SeparateFields.SelectEvery(4,0,3)
Weave

This avisynth code above (which came from avisynth.org) is excellent for taking a pal source and converting it to ntsc (29.97).

To be specific it works like this:

Step 1--
PAL=25fps/576i source is deinterlaced directly to (50/2)fps/480p by seperating the two interlace fields of the pal source (effectively 50fps/288p) and expanding those 288 scan lines into 480 scan lines.

Step 2--
Horizontally stretches the image to fit the DVD standard which is width=720 (in all formats).

Step 3--
This framerate conversion (60000 / 1001 = 59.94) makes the video like (59.94/2)fps/480p.

Step 4--
I dunno whut dis do... !?!

Step 5--
(59.94/2)fps/480p becomes 29.97fps/480i... NTSC. That's right, it reintelaces it into NTSC's interlaced form.



Does this work for you?

[adam]

The above script should work but its really only useful for an interlaced source which you almost surely don't have. 25fps progressive sources should simply be slowed down to 23.976fps and then have the pulldown flags enabled. See, your source was most likely sampled at 24fps to begin with and then sped up to PAL. You simply want to reverse the process. You will have to slow your audio down too though. You could use Besweet's PAL->NTSCfilm option for this.

The above script converts directly to interlaced NTSC by (actually more than) doubling the fields and then selecting them in a pattern. This will result in less smooth playback then if you converted properly to NTSC (slow down to NTSCfilm then telecine to NTSC) and you will also be taking a progressive source (frame pictures) and encoding it using field pictures, which inherantly requires more bitrate to achieve the same level of quality. I'm not sure without doing some testing but I believe one advantage with this method is that you would not need to adjust the audio...but that's not worth it in my opinion.

In other words, if your source is progressive than PAL->NTSC and vice versa conversions should just be a simple slow down or speed up by 4%. Only when the source is interlaced does this become impossible since the pulldown can't work on an interlaced source. THAT'S when you'd want to resort to a script like the one sweetfreek posted.