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The illusion of DVD, 24P and NTSC frame rates re: conversion for portables


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#1 of 1 OFFLINE   Keith Paynter

Keith Paynter

    Screenwriter



  • 1,830 posts
  • Join Date: Mar 16 1999

Posted January 20 2014 - 11:35 PM

I have several DVD's in my collection, and have been trying several different third party software applications with which to convert my discs into iTunes-acceptable media, simply because I would like the option of portability, and would like to donate many of the DVD's I have re-purchased as Blu-ray titles to my local public library.

 

This is not meant to endorse De-CSS or other decryption software.  This was just the result of some technical observations.

 

In the days of videotape and laserdisc, analog video for NTSC required a playback rate of 29.97 frames per second, since signal operates on a 60Hz bandwidth. Unlike PAL, which works at 25 fps/50Hz, and can easily manipulate a better film transfer by simply raising the speed of film by approximately 4%, from 24 to 25fps, NTSC conversion of 24fps utilizes a "3:2 pulldown" and duplicates frames and uses interlacing of video frames in order to make the transition appear smooth.

 

What is sometimes forgotten is that professional, official studio transfer of film to digital video for DVD is done at 24p (technically 23.97) fps, and the video signal is actually converted to an interlaced signal for 60Hz NTSC televisions, including today's flatscreen HD televisions, which receive signals at 30i and 60i fps. By the same token, it is not a complicated process to "upconvert" DVD for 1080p HDMI. It still requires interlacing for a 60Hz, pixel-based HD television.

 

What this means is that anyone who is using conversion software for viewing their movies or videos for portable devices will get the best results for their movie transfers not by using an NTSC video framerate of 30fps or 29.97 fps, but at 24 or 23.97fps if the application allows it, which will virtually eliminate the jerkiness associated with the wrong frame rate.  Videotaped programming (concerts, television programs, etc.) that is captured at 29.97fps should likewise be captured at its native framerate for a smooth appearance.

 

Visually, the results can be almost as good as (for example) any SD iTunes movie purchase, which still exhibits digital artifacts when played on either a PC, or HDTV via AirPlay to an AppleTV box. In the end, It was not the software that made the picture look bad, but the lack of ability to capture it at the correct speed(s). 

 

I'm not going to endorse any particular software program. I am simply using these findings to create better-playing media for my portable needs.


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