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View Full Version : PAL and NTSC running times - what a spin-out!


Prizm
20th January 2002, 17:41
I'm a bit confused about PAL and NTSC running times. It's supposed
to do with the frame rate, right....well, let's take Shrek - 90
minutes in NTSC, 86 minutes in PAL.
Does that mean I finish the movie 4 minutes faster if I watch the
PAL version? :confused: It's very paradoxic.

If the movies are the same length (no cuts), how can one finish
faster than another?

Prizm

Doom9
20th January 2002, 18:01
a movie is shot at 24fps, right? in order to make it compatible with ntsc tvs (60Hz) you have to go thru a complicated field repetition called telecine. for pal it's easier as they're 50Hz.. or 25 fields per seconds. So.. they take the 24fps source.. and speed it up a bit so that you end up with 25frames per seconds, and then you split these into 2 fiels each giving you 50 fields/s which is what pal tv need. so.. taken from the same source and with no cuts pal movies will always be shorter than ntsc movies.

MxxCon
21st January 2002, 06:45
hahah, i never thought of it that way :)
i guess it's more time efficient to watch pal movies :)

Prizm
21st January 2002, 11:21
Doom9 -

But how does that translate into additional minutes? If telecining
is repeating fields to make 30fps - wouldn't the amount of UNIQUE
frames be exactly the same as the 25fps version? (Except that there
is a repeating of certain frames) If that is correct, there is still
the same amount of footage per second, because:

1. PAL is playing at 25fps - fine.
2. NTSC is repeating certain frames, yet playing at *30fps* - slightly faster to *make up* for the repeated frames - therefore it
virtually plays at the same speed as PAL.


Sorry, I'm still trying to grasp this.

How can a 2.5 hours movie be 15 minutes longer in NTSC? What do you
american viewers do in that extra 15 minutes? :)

Prizm

stankus
21st January 2002, 12:56
Originally posted by Prizm

How can a 2.5 hours movie be 15 minutes longer in NTSC? What do you
american viewers do in that extra 15 minutes? :)
Prizm

The answer is pretty simple:

Source = 24FPS

Now, to play that on an NTSC system which is 60 *fields* per second it is "telecined" (transferred from film to video) with "3:2 pulldown". That means that 1 frame is played for 3 fields, and the next for 2. The result? 24 frames fit right into 60 fields.

To play that on a PAL system which is 50 fields per second, it's not so simple, because the only way to make it work would be to repeat a frame. They don't do that. The solution is that the film is sped up by four percent. Obviously, that means that the movie is shorter.

The NTSC and film versions are the same length. There are no "extra frames". The PAL version is shorter because it is played faster.

The nice thing about a PAL video is that you don't need to REVERSE the telecine process to get the original frames because it's just played faster. So for example, when I used a PAL DVD, I just changed the framerate (in VirtualDub) from 25 to 24FPS. Then I loaded the audio track into Cool Edit and slowed it down to the original speed (that could be the hard part). The result was better than my DVD original. ;p

(Film is actually 23.976FPS and NTSC is 29.97FPS.. but that isn't important for this explanation)

Kedirekin
21st January 2002, 13:57
I think the one obvious thing that is missing here is that PAL actually plays slightly faster - the 24-to-25 fps speed up means that people and actions move 4% faster. In other words, a 1 minute scene that took 1 minute to view in the theatre only takes 57.6 seconds to view via PAL playback.

On the other hand, the IVTC process for NTSC slows the movie down very slightly. As outlined above, the IVTC process first does 24-to-23.97 fps slowdown, then inserts fields to get to 29.97 fps (and in terms of minute-to-minute changes, the field insertion is a null operation). In other words, that same 1 minute scene takes 60.075 seconds to view via NTSC playback.

Prizm
21st January 2002, 15:54
Ok, now we're getting somewhere. When Doom9 said the 24fps was sped
up into 25fps, I thought he meant *converted*, not actually sped up.

So when the audio is sped up, is the pitch increased; or are samples
deleted to preserve the pitch yet shorten the length? (stankus, you
would understand this question since you use Cool Edit)

Prizm

prr
21st January 2002, 16:10
If hardware/software supports, audio is speed up without any changes in pitch. If hw/sw does not, pitch is increased a bit.

trbarry
21st January 2002, 17:30
On the other hand, the IVTC process for NTSC slows the movie down very slightly. As outlined above, the IVTC process first does 24-to-23.97 fps slowdown, then inserts fields to get to 29.97 fps (and in terms of minute-to-minute changes, the field insertion is a null operation). In other words, that same 1 minute scene takes 60.075 seconds to view via NTSC playback.

IVTC stands for "Inverse Telecine" or the process of reversing Telecine. I think the telecine does not first speed things up to 24 fps, it just splits each frame into 2 fields and then adds one extra field for every 4.

So now you have 2 * 23.976 * 1.25 = 59.94 fields / second or 29.97 video frames / second but the sound is still played at the same rate. And the IVTC process can remove the extra fields, but the sound is still played at the same rate.

All the above is for NTSC. In PAL I guess they actually do speed up the playback by a 25/23.976 ratio after splitting the frame into 2 fields.

The strange cases are where it is first telecined as NTSC and then converted to PAL. I still don't understand all the ramifications there but I know they create extra problems for us.

- Tom

Kedirekin
22nd January 2002, 00:30
You're right. My mistake. I should have said 'in the telecine process they first slow things down slightly'.

qthesnake
23rd January 2002, 07:19
hey:

about the pitch... there is a very rutine and easy process, which i forgot his name, that fixs the pitch problem when converting a movie into pal... the studios do that and you get a movie has the "same" audio track, but i guess it has a few samples less..

Q.

ppera2
23rd January 2002, 15:53
When timestreching audio with good software you can choose between preserve pitch or not. In first case it must cut some samples of course.
For example in Wavelab you can choose between 3 quality grades for processing.

zeronegative
24th January 2002, 09:46
About a change in pitch; I'm pretty damn sure that audiotracks in series sound different in the States than they do in Europe.

I'm a pretty big Simpsons/South Park fan, and I've seen damn near every episode here in Holland. When I was on holiday in the States it immediately struck me that it sounded slightly different, the voices were a bit lower (as I recall). So obviously, even if they do a pitch-correction, it doesn't correct it for the 100%.

KyleK
4th March 2002, 06:14
hehe, we germans don't care, because everything gets dubbed ;)


KyleK @ FNW

kermit70
4th March 2002, 11:01
Originally posted by qthesnake
hey:

about the pitch... there is a very rutine and easy process, which i forgot his name, that fixs the pitch problem when converting a movie into pal... the studios do that and you get a movie has the "same" audio track, but i guess it has a few samples less..

Q.

yes, it would be easy to at least correct the pitch in PAL transfers, but they very rarely actually do it. I have a couple hundred PAL transfers (vhs, ld, dvd) and not one of them has the pitch corrected. Comparing some of these with their NTSC counterpart, you can hear that they are considerably higher pitched (sounds very bad with music one knows and already high (female) voices). Anyway, correcting the pitch is only half of the problem - they would still play too fast. Thankfully, if you're making a DivX, there are ways around this.

kermit70

qthesnake
4th March 2002, 13:22
i hate attacking, so i will do this as easy as i can...

that is bullshit!
i have about a hundred PAL DVDs, and all of them sound, and have, the same PITCH as the US version! i don't only listen to them, since my main interest is sound sampleing for remixing, i use audio encoding software that visualize the dbs and pitch and i compered some DVDs (Matrix, Charlies angels, the green mile, the watcher) and the NTSC and PAL sound streams are IDENTICAL in pitch... i am talking about DVD only, i never checked TVs, although i download every SouthPark episode there is, ripped from a tv in USA, and watch a few SP episode here in europe, and the voices sound the same...

kermit70
4th March 2002, 17:56
Originally posted by qthesnake
i hate attacking, so i will do this as easy as i can...

that is bullshit!
i have about a hundred PAL DVDs, and all of them sound, and have, the same PITCH as the US version! i don't only listen to them, since my main interest is sound sampleing for remixing, i use audio encoding software that visualize the dbs and pitch and i compered some DVDs (Matrix, Charlies angels, the green mile, the watcher) and the NTSC and PAL sound streams are IDENTICAL in pitch... i am talking about DVD only, i never checked TVs, although i download every SouthPark episode there is, ripped from a tv in USA, and watch a few SP episode here in europe, and the voices sound the same...

If you believe this, be my guest - obviously you need to have your hearing examined, no offence. 99% of PAL transfers (yes, that includes DVD's) are NOT pitch corrected during speed-up, this is a fact. Check similar discussions on the usenet for further proof.

kermit70