Good Idea to convert every 25fps Movie to 24fps?

[kagoru]

As I read in some articles the movies we watch at the cinema are all 24fps. PAL movies are played back at 25fps though. Therefore the movie is some minutes shorter and the sound has a somewhat higher pitch and is also faster! So why stick to 25 fps?

To get a 24 fps movie you could use avisynth's ChangeFPS(x). But how would you do the sound?

[Foo]

There is no need. There isn't a huge compression benefit in going from 25fps to 23.976 (properly IVTCd NTSC source). And since this is a DivX forum, it would be a real waste of effort on your part IMO. The time you'd really want to do this is if you wanted to make NTSC (S)VCDs from PAL sources. DivX doesn't care about NTSC/PAL, so just enjoy not having to IVTC all of your sources :D .

foo

[kagoru]

I know that there wouldn't be ANY compression benefit since the frames are still the SAME. They are only played back at a somewhat slower rate. The advantage though, I think, is that you see the movie like you would in the cinema!

[Foo]

Actually there *WOULD* be a compression benefit, because there are less frames to encode. The point is that it would be small, and not worth the time involved in the conversion process. As to the other part, your eyes couldn't tell a difference, so again it isn't worthwhile. If you could see some amazing difference between 23.976fps and 25fps, you think NTSC users would accept 30 (29.97)fps :p ? We MUST do 3:2 pulldown removal to remove interlaced fields (deinterlacing looks like crap in comparison). We also get a nice compression benefit because there are less frames to encode once you drop the interlaced and duplicates. So to answer your question again, NO you shouldn't convert all 25fps PAL sources to 24fps. The ONLY time this is really important is when trying to create NTSC (S)VCDs from PAL sources.

cheers,

foo

[UHT]

there would be the same amount of frames, think about it

[Foo]

Originally posted by UHT
there would be the same amount of frames, think about it

Actually I did :) . I'm talking about PAL sources where there is a duplicate frame added for every 24. So you would nuke this frame to bring the framerate back down. If you are just talking about slowing down the playback, then of course it won't be different, but again there isn't really any good reason to do it that I know of.

cheers,

foo

[UHT]

from what was originally posted that seemed to be what he was wanting to do

[gabest]

Slowing down to 24fps could be a real benefit when you're watching your favorite movie and want to enjoy it even longer :D

[Slogra]

That's not a good idea. The biggest problem is the sound. The sound has been speed up with professional equipment, often with pitch correction. When you speed it down again, it won't sound good at all. Trust me, i've tried it.

[kagoru]

Thanks for your replies!
PAL movies DON'T have a duplicate frame! They're only played back at a higher rate. So for 24fps I would, as mentioned correctly, just slow down the movie by 1/25. There wouldn't be ANY compression benefit because I keep ALL the frames.

I thought that the sound would be the actual problem since it is not only speed up but probably also professionally edited as Slogra already said (Do they lower the pitch of the actor's voices or what do they do?). I myself CAN tell the difference when I watch the movie (American Psycho i.e.) and listen to a background sound (Hip to be square i.e.); I can tell the speed difference of the song. It does not really bother me, but I just wanted to show that you CAN tell the difference! (Try it yourself!).

For the sound: Coulnd't you just put the sound in your .avs-file with your movie and the change the fps? [Can I put an mp3-file in an .avs-script).

[Slogra]

Originally posted by kagoru
For the sound: Coulnd't you just put the sound in your .avs-file with your movie and the change the fps? [Can I put an mp3-file in an .avs-script).

I've got no idea how avs files work but i know this:
When you lower the fps, the length of movie will be longer. So the the length of the sound HAS to be longer too. So you WILL have to slow it down.

Sometimes they just speed the sound up, so it'll have a higher pitch (you might be able to slow down the sound of these movies). And sometimes they lower the pitch too (don't try to slow it down, cause it'll be horrible). Problem is: how do you tell which movie has pitch correction?

[kagoru]

That is obviously true. Does anyone know something about avisynth? Can I put a sound-file in a script and use the ChangeFPS function to make the sound longer?
Would there be any degration in the sound quality if JUST slow it down?

TIA.

[Slogra]

I don't if you read my editted post or not, but:
- When the sound has pitch correction you should not slow it down.
- When the sound of movie is just speed up, then you should be able to just slow it down with nice quality.

[Doom9]

besweet supports audio pitch changes.. but unfortunately only in the other direction (nstc -> pal). Honestly, I don't think it's worth the time... I admit the possibility that you can hear the difference on a sound / melody that is very familiar to you or if you do a 1on1 comparison, but other than that it's a lot of work for a small gain

[b0b0b0b]

If you're going to watch a movie in its original aspect ratio, why not go the extra mile and watch it in 24fps, at the original speed?

I bet that Europeans, as a result of watching movies sped up, grow up with a completely different sense of comic timing.

[b0b0b0b]

I bet that Robin Williams comes across as a superhuman maniac, even moreso.

[kermit70]

I can't believe the amount of halftruths and plain BS that gets thrown around here.

Speeding down PAL movies to their original speed is quite easy. I've been doing it for the last year or so. Actually the only reason I started doing DivX rips is that I could finally get rid of this damn speedup (which *Is* noticable, especially with music or female voices). As far as the alleged 'pitch correction' that was mentioned here, I can only say that I encoded about 100 movies so far and not one of them had any pitch altering done to them after the fact (i.e. - they sounded perfect once slowed back down). So anyway after quite a lot experimenting I came up with the following procedure, that has worked brilliantly so far.

First, get azid, lame, ssrc, avifrate, wavefix & nandub (all but wavefix downloadable here)

1. Rip the movie normally at 25fps, demux the audio.

2. Use AVIfrate to change the avi to 24fps (this is a simple header change - the movie size stays exactly the same, it just gets played back at a slower rate).

3. Convert the audio to wav using azid. Now you got a nice big 48KHZ wav file.

4. Slow down the audio using ssrc. In order to do this simply change the sampling rate from 48000Hz to 50000Hz (this is exactly the 24/25 ratio of the PAL-Speedup).

5. Now, if you would play the resulting file, it would still be the same speed, but simply had more samples. So you have to change the wav header back to 48000Hz using wavfix. Now play it and you will notice that it's finally at its correct speed.

6. Finally, just mp3 it using lame and mux it to the avi using nandub.

This sounds more complicated than it really is, but once you get the hang of it, you end up with a perfectly pitched rip that's even more accurate than NTSC rips which are slightly too slow (23,97 v. 24fps).

Hope this helped,

kermit70

[lucaramel]

I think no one has understood the problem. Slowing down the movie is pointless. In a cinema, movies are played with a 24fps rate (well actually it's doubled to 48fps), but movies are played at 25fps on PAL systems, because it works in 50Hz and a video image is made of 50 fields (2 fields make 1 frame, so 25fps). When you see a movie on your TV, yes it's a bit shorter because it's played faster. The difference is like 2 1/2 mn for one hour.
You can still slow down the movie because it's a divx, but you'll just lose time for nothing.

Besides, to reply to bobobob, you say European grew up with films sped up because movies are played at 25fps instead of 24. What you can say about Americans, whose films are played at a 30fps rate ? That's quite a difference here...

[gabest]

1. In the first paragraph you were talking about the same thing as the rest here.
2. I'm sure that you don't know one little important thing about that "30fps rate" :)

[lucaramel]

1 -I know but no one seemed to understand that it's pointless and time-consuming

2 - Well what ?

[gabest]

2. I hoped that you would find it out by your own, but anyway. 24fps movies are slowed down to 23.976 and converted to 29.97fps by adding extra frames built from the existing ones. There is no speed up for ntsc.

[lucaramel]

Good point... but still it was made to be funny for bobobob so I guess you can forgive me ;)
Well, movies aren't sped up but they're slowed down so there's still a difference, is there ? :)

[ppera2]

Couple notes here:

In AVISynth you need to use AssumeFPS and not ChangeFPS command, because ChangeFPS works by drop/insert frame (see manual).

4 % speed up is not too noticable, but if you heard sound in original you will feel difference. So, whole thing is only for 'Mozart-ear' perfekcionist people.

Actually DivX at 25 fps will be little shorter than at 24 fps, because of shorter audio. So, maybe speed up has some sense, if you have problem to fit it to CD.
And by me, many movie will be much more enjoyable when play it faster, not just 4% :D .

[Zhnujm]

besides those audio problems (or no problems), if you watch 24fps files on a tv you wont get a smooth video. think thats a bigger problem than a few minutes shorter movie. (well, if you use a tv for watching)

[b0b0b0b]

I bet that mp3 is so smart that if you stretched the audio by 4% that it would realize this and use it to its advantage. I bet there's no space loss whatsoever.

I guess this post is a troll but hey I'm at work and I am sick of it.

[Slogra]

Originally posted by Zhnujm
besides those audio problems (or no problems), if you watch 24fps files on a tv you wont get a smooth video. think thats a bigger problem than a few minutes shorter movie. (well, if you use a tv for watching)

Very good point :cool:

[ftack]

Originally posted by b0b0b0b
I bet that mp3 is so smart that if you stretched the audio by 4% that it would realize this and use it to its advantage. I bet there's no space loss whatsoever.

I guess this post is a troll but hey I'm at work and I am sick of it.

The discussion here IS relevant for the perfectionists among us. The speed of movies IS slowed down a tiny bit for NTCS and IS accelerated by 4% for PAL movies, so the cinephilics among us now have the tools to restore these movies to perfection.

There are no benefits in terms of compression for the video, because we're talking the same number of frames. However, for slowing down a PAL movie to 24 fps, the audio will be 4% shorter and hence take up a tiny bit less space. Peanuts, however, compared to the size taken by the video stream.

Bottom line: there is no point of changing the speed of a DivX movie, unless you're a movie adict-perfectionist who wants to see the movie with exactly the original speed.

I am currently struggling with this problem in the oposite direction, converting an NTCS movie to PAL for transferring to VCR. Speeding up the audio with no digital artifacts is my problem, but I am not desparate yet :-)

[ppera2]

Originally posted by ftack

...
However, for slowing down a PAL movie to 24 fps, the audio will be 4% shorter and hence take up a tiny bit less space....


Slowing down and will be shorter ??????? Think again about it.

[ppera2]

Originally posted by kermit70
I

Speeding down PAL movies to their original speed is quite easy.
header back to 48000Hz using wavfix. Now play it and you will notice that it's finally at its correct speed........
kermit70

I started to watch DivX movies on my PAL TV, and have problem with it, as Zhnujm pointed to it. I have lot of them at 23.976 fps. Probably speeding up them to 25 fps will help. Audio is in VBR MP3 in many cases. Could you give me some advice how to 'speed up' it without much quality loss. Must I decode it first to PCM WAV or... ?

[kermit70]

Originally posted by ppera2


I started to watch DivX movies on my PAL TV, and have problem with it, as Zhnujm pointed to it. I have lot of them at 23.976 fps. Probably speeding up them to 25 fps will help. Audio is in VBR MP3 in many cases. Could you give me some advice how to 'speed up' it without much quality loss. Must I decode it first to PCM WAV or... ?

Well, same principle applies. Change the avi header to 25fps (w/ avifrate). Convert the mp3 to wav and speed it up accordingly. 23,976/25 = Factor 0,95904. The best wav to go here would be to use a wav editor like CoolEdit to compress the wav by the above factor. Then just re-mp3 it and mux it with nandub.

By all accounts it should work, don't know why you want to do it though. I would rather have slightly jerky playback than speed-up audio. I only watch DiVX movies on my 22" Monitor anyway, so no problems with different frame rates.

Hope this helped,

kermit70

[Triggerle]

Where can I find the previously mentioned wavfix?

I tried searching with Google and I also checked several sites about divx encoding, but I can't seem to find this program.

Thanks in advance,

Triggerle

[kermit70]

Originally posted by Triggerle
Where can I find the previously mentioned wavfix?

I tried searching with Google and I also checked several sites about divx encoding, but I can't seem to find this program.

Thanks in advance,

Triggerle

Go here: http://www.celestialaudio.com/freebie.htm

kermit70

[movmasty]

wow, what a long thread! but finally i am at the end, and can say my opinion.
you need both the 25-->24 to restore the original lenght or the 24-->25 to watch on pal tv.
fps change can easily be done with vdub in video/frame rate,then direct copy.
for audio i use sound forge, it can either change or not the pitch when changing duration.
video speed change is only noticeable beyond 10-15%, audio pitch,instead,is very sensible to speed change,beyond 2% i think,
but i bet that pitch doesnt get changed when fps goes from 24 to25
coz this is a very easy thing to do.

often i like to do more
if i have a 25fps source,i make a movie at 20fps,
where some part that i think needs,is slowed from 25 to 20fps
some other part is speeded to 30fps and become 20fps with frame deletion.

this is a real "speed customization" !

[ppera2]

There is a nice Media Player plugin DivXG400. Newer versions can solve problem of playing 24 fps material at 25 fps (on TV).
It works by speed up while maintain audio sync. For me it is very good solution. Kermit70 probably wouldn't like it, but for my old ears... :p .

[Triggerle]

Just to throw a quick Thanks at kermit70. I used the method you described and it worked like a charm. I will slow down all of my PAL dvds now. Oh joy!

Triggerle

[movmasty]

seems that i cant play waves "fixed" with wavfix.

[smok3]

nice method kermit70, but isnt there a player that can slow down the sound by that 4,x % on playback ?