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Topic: DVD formats NTSC vs PAL and the 'cut film' argument

6th Sep 2016, 2:10 AM
	albert oh well, la di da Member since Aug 2013 1345 Points	I am writing these notes as a reference if anybody has the usual question on why Region 1 DVDs appear to have longer versions of a film in comparison to Region 2 DVDs. (And I'm sure this question will pop up if it has not already done so). The short answer is DVD encoding formats. Region 1 DVDs will pretty much always be in the NTSC format, while Region 2 DVD will usually be in the PAL format, and the PAL format runs a film slightly faster than expected. So for example a film which is exactly 90 minutes long will run for 86 minutes and 24 seconds on a PAL format DVD, whereas on a NTSC format DVD it will run for 90 minutes and 5.4 seconds approximately. Now the long and boring answer. Actually if you want the correct long answer then wikipedia will have the details, but it is a massively complicated thing so I will again summarize. So you may be wondering why half the world uses NTSC and some countries use PAL (or other TV formats) and why did the division come anyway? Well its all down to your AC electricity power supply, for instance in Britain we have a 50 Hz supply and in USA it is 60Hz and many electrical device were designed to rely on the AC cycle of the electrical current in order to function correctly, like a television set. An old PAL television in Britain refreshes its image 25 times a second (its actually 50 interlaced times a second), and in America an old NTSC television refreshes its image roughly 30 times a second (60 interlaced) thus matching the relevant AC cycles. Modern TVs will probably use a transformer to convert an AC power supply into DC and have internal electronic components which handle TV signal formats without relying on cycles on the AC power supply to get timings. But because of the history of power supplies we have the NTSC vs PAL situation on DVDs. Now old films. OK there are lots of different formats to old film, but what we are really interested in is the frame rate and for most 35mm film the frame rate was normally 24 frames per second (other size film and different frame rates exist). So the most straightforward conversion for a film transfer to DVD is to match frame to frame on PAL, [thats the simplified technical answer]. The maths for a film which is exactly 90 minutes goes 90minutes x 60seconds x 24frames = 129600 frames. Then into PAL its 129600frames / 25frames / 60seconds = 86minutes and 24seconds, so it looks like the film has lost 3minutes and 36seconds but in reality there is nothing cut at all. NTSC is more problematic as we cannot match film frame to NTSC frame without it looking noticeably speeded up. So the conversion is trickier, but although NTSC is approx 30 frames per second it is actually 60 interlaced (half) frames per second, and 60 divided by 2.5 gives 24, matching the film's frame rate, so conversion is possible. The downside to this conversion is that the interlaced crossover between frames can result in noticeable defects where any motion is happening on screen. I would like to report that a 35mm film converted to NTSC format runs for exactly the same amount of time, but I suspect that this is not the case. People do insist on this 'frames per second' measurement for film but NTSC does not compute too well and is commonly badly quoted as approximately 29.97 frames per second when it would be better described as 30 frames per 1.001 seconds. So the maths for a film which is exactly 90 minutes should include an adjustment where every second is multiplied by 1.001, hence 90minutes x 60seconds (/ 1) = 5400seconds. Then into NTSC its (5400seconds x 1.001) / 60seconds = 90 minutes and 5.4 seconds, which may inadvertently seem like there are a few seconds of extra footage but in reality there is not. Anyone still awake? Oh and by the way, the speeded up PAL format is the reason why lots of musicians prefer their music videos to be in NTSC format, cos the pitch will all be wrong in PAL. Edited by albert on 6th Sep 2016, 2:16 AM