How is 25fps to 30fps possible with out a movie speedup?

[teamdork]

How is it possible to go from 25fps to 30fps with out making the movie play in fast motion? In other words: If a movie is encoded in PAL format and it plays at 25fps and finishes in exactly 2 hours, then how could you speed it up to play 30 (NTSC) frames per second and still expect it to end in exactly 2 hours? Wouldn't you have to add frames that were not part of the original movie to make this work? Like duplicate frames? And wouldn't this make the movie play back appear all jerky and messed up?

I ask because there are DVD's on AmazonUK that are not available in America, I would like to order them and change from PAL to NTSC if this is posible and the quality is still good.

Thank you for any information

[Nilfennasion]

Jerkiness is a fact of life with NTSC video. The only things that do not appear jerky in an NTSC transfer are things that were filmed in NTSC (television shows, for example).

To answer the question, 20% of the resolution is discarded and five extra frames per second are added. That's how you convert PAL into NTSC.

[lordsmurf]

PAL played on a NTSC player is NTSC-50. No jerkiness. Just like NTSC on PAL is PAL-60. Screwball type stuff.

[rgs_uk]

Presumably there are occasional double/merged frames though? If a Pal TV show has only 50 fields and has to be increased to 60 fields, there must be?

[Nilfennasion]

PAL played on a NTSC player is NTSC-50. No jerkiness. Just like NTSC on PAL is PAL-60. Screwball type stuff.

I don't know where you get this from. Both formats have to be converted in order to be played on the other system. Conversion, by definition, introduces artefacts. There are several DVDs in Australia that have been converted from NTSC to PAL, and the result is a mess. It is fine to look at when the picture isn't moving, but as soon as it does, it blurs into a half-frame mess.

http://www.michaeldvd.com.au/Reviews/Reviews.asp?ReviewID=311 This shows an excellent example of what happens when an NTSC to PAL conversion is handled badly.

I'm just flabbergasted at this idea that you can just play one on the other. Many PAL TVs cannot sync to a 60Hz signal.

[OneCardShort]

lordsmurf wrote:
PAL played on a NTSC player is NTSC-50. No jerkiness. Just like NTSC on PAL is PAL-60. Screwball type stuff.


I don't know where you get this from.

Lordsmurf is right about this video standard (pal 60). It is used in Europe on multisystem tv's and dvd players. It's why I can take my ntsc dvd's with me when I visit my family in eastern europe and play them there.

[Nilfennasion]

The point I am trying to make is that in order to be played back as PAL-60, NTSC has to be converted. There is no way around it. You can't just say "it's PAL because it is being output to a PAL television". It doesn't work like that.

There's also the fact that regardless of what the signal is, it is far better to play it back in its native format.

[bugster]

You can't just say "it's PAL because it is being output to a PAL television". It doesn't work like that.

Hmm, well, you can, sort of. The problem here is that DVD-video does not really care about PAL vs NTSC as such. The main problems are frame rate and resolution.

As you know, NTSC is ~30fps (or 60 fields per second). So, if you take a DVD-video, which is digital, and use it to generate a PAL type analog signal (such as on a composite or s-video connection from your dvd player to your TV) but with 60 fields per second (instead of the 50 fields that PAL would normally generate), you get PAL-60. Many, if not most, PAL TV's will handle this quite happily.

You can do the reverse with a PAL DVD-Video and NTSC, generate NTSC-50. It seems though that less NTSC sets will handle this correctly.

The other way of converting PAL to NTSC is to slow the PAL movie down to 23.976fps and add 3:2 pulldown flags. Obviously the audio length will need to be adjusted. You probably wouldnt notice the slowdown either.

[iantri]

Getting back to the original question,

How is it possible to go from 25fps to 30fps with out making the movie play in fast motion? In other words: If a movie is encoded in PAL format and it plays at 25fps and finishes in exactly 2 hours, then how could you speed it up to play 30 (NTSC) frames per second and still expect it to end in exactly 2 hours? Wouldn't you have to add frames that were not part of the original movie to make this work? Like duplicate frames? And wouldn't this make the movie play back appear all jerky and messed up?

Depends on what you call jerky. Generally, the best way to do this conversion is to undo the process film undergoes in PAL (i.e. undo the 4% speedup by changing the frame rate to 23.976fps and resampling the audio. Yes, I know that is 4.1%. The extra .1% is the slow down that film actually has in NTSC). Then you telecine the film to 29.97fps, whether by actually performing the telecine or creating a 23.976fps MPEG-2 with the pulldown flags enabled, which causes your DVD player to do it.

This will look exactly the same as any movie shot on film looks normally with NTSC, that is to say, slightly jerky because of the 3:2 pulldown. It will be identical looking to a North American DVD, though.

The movie will actually be a few minutes longer, but this is normal -- the DVD, unless it was shot on video, would have originally been this length anyway, had it not been converted to PAL.

[adam]

The point I am trying to make is that in order to be played back as PAL-60, NTSC has to be converted.

No it doesn't, that is the whole point of PAL 60Hz. The NTSC standard only supports 60Hz. If you want to play PAL sources on an NTSC playback device it must be converted, period. PAL can support both 50Hz or 60Hz. Older hardware could only do 50Hz, but most of this has been phased out. Most PAL equipment these days supports both 50Hz and 60Hz. If you have 60Hz NTSC sources simply play it on PAL equipment that supports PAL 60Hz and no conversion is done and no quality is lost. The hardware simply supports both standards.

[Nilfennasion]

Frame rates are only part of the puzzle. To make a PAL TV sync to an NTSC signal, you have to add 96 lines to it. This cannot be gotten around - you cannot author a disc to contain a 576I video and a 480I video without encoding the same video twice, effectively halving the amount of space you can devote to it.

Reducing a signal from 576I to 480I is, by definition, a conversion.

I have a friend in the USA whose player spits out the discs whenever they are in PAL, so it's not as simple as is being made out (sadly).

[bugster]

I have a friend in the USA whose player spits out the discs whenever they are in PAL, so it's not as simple as is being made out (sadly).

So, one player does not prove anything.

With SOME DVD players and SOME Tv's, you can play PAL DVD's and output NTSC-60 signals. How they actually resize (or crop) the image I don't know, but remember we are talking digital video to analog signals. Once the signals enter the analog domain its a completley different set of problems.

What we are saying it IS possible to play PAL DVD's on NTSC TV's (and vice versa) without frame rate conversion, if you have the right players/TV. Yes, some image resizing may be required, but that will have much less efect on quality than framerate conversions.

[Nilfennasion]

Okay, now I gotcha. The problem boils down to communication. The original quote I was responding to:

PAL played on a NTSC player is NTSC-50. No jerkiness. Just like NTSC on PAL is PAL-60. Screwball type stuff.

Now, obviously, some words needed to be added to this in order to make it work. "On some TVs and players" would have been a great start. It's hard enough dealing with people who don't know what they're doing without them reading things like this and getting the wrong idea, you know.

As for how they "resize" the image, they don't. When you go from PAL to NTSC, an algorithm discards certain lines from the original image. If the processor doing it is well-made, then the result is certainly watchable. The opposite applies to NTSC to PAL. They use an algorithm to add lines to the image by duplication. It's a similar principle to how they make 16:9 images appear on 4:3 displays without vertical elongation.

[spiralnebula42o]

Depends on what you call jerky. Generally, the best way to do this conversion is to undo the process film undergoes in PAL (i.e. undo the 4% speedup by changing the frame rate to 23.976fps and resampling the audio. Yes, I know that is 4.1%. The extra .1% is the slow down that film actually has in NTSC). Then you telecine the film to 29.97fps, whether by actually performing the telecine or creating a 23.976fps MPEG-2 with the pulldown flags enabled, which causes your DVD player to do it.

This will look exactly the same as any movie shot on film looks normally with NTSC, that is to say, slightly jerky because of the 3:2 pulldown. It will be identical looking to a North American DVD, though.

The movie will actually be a few minutes longer, but this is normal -- the DVD, unless it was shot on video, would have originally been this length anyway, had it not been converted to PAL.

-iantri


Ok iam cofused about this whole process. Am I supposed to encode my Pal source using 23.976fps then take my new encoding file and use this telecine thing to change it to 29.97fps? Also what about these pulldown flag things when am I supposed to use these? is this all one encoding process or several process's? Iam really confused on this whole thing. I use TMPGEnc and I know it has that telecine thing your talking about I just don't know how to do it, could you by any chance re-write how to do this process but just make it more detailed or put it in steps or something cause iam really lost? will this process hopefully eliminate the slight jerkyness that you sometimes get from converting PAL to NTSC?

-Jay

[iantri]

OK. Here it is, step by step. There ARE guides in the guides section, but I will run through it step-by-step. You will need AviSynth. (http://www.avisynth.org I think) and a DVD ripping program, plus something to demux the VOB files and BeSweet. AviSynth is a powerful frameserving tool that allows you to write scripts to process video in real-time, without temporary files.

This is rather complicated when dealing with DVDs. I'm flying by the seat of my pants here -- sorry if there are typos.

First, you have the 25fps PAL source (I'm assuming it is progressive; that is to say, a movie) DVD. Rip the DVD and demux the VOBS. You should now have several files, the video, the audio, the subtitles, etc.

Write an AVISynth script like this:

MPEG2Source("pathtofile.mpg")
BicubicResize(720,480) # assuming the video was full D1 -- 720x576.  There is actually a slight aspect error introduced here, but what the hell.  Widescreen movies will require you to make the appropriate calculations.
AssumeFPS(23.976)

Encode a video-only file (of the same bitrate as the original, that way it will fit) in TMPGEnc.

Use BeSweet's OTA adjustment to go from PAL -> NTSC, and it will slow down the audio appropriately. BTW, Re-encoding the AC3 audio is a pain and the output isn't 100% compatible.

Mux it all back together and burn.


Trust me, it is easier just to get a cheap DVD player that can do a rough PAL to NTSC conversion on the fly!