How to correct "fake FPS"

[ridibunda]

The issue is a little bit weird.

I downloaded a HD video. MediaInfo and PotPlayer report it as 25 FPS.

I also have PAL retail DVD of that video. You all know that PAL is 25 fps.

PAL DVD duration is 01:17:25.

HD stream duration is 01:21:00. I saw that HD stream did not contain any extra scenes.

So I found out that HD stream is actually 23,976 FPS. That explains the time difference.

PAL video: 4645 seconds x 25 FPS = 116125 frames

NTSC: 4860 seconds x 23,976 FPS = 116523 frames

It is an almost match. Extra 400 frames (about 15 seconds) belong to a opening-credits segment which does not exist on DVD.

You see that there is a fake 25 FPS there. Stream service did it wrong. Why stream a 23,976 FPS video as a 25 FPS video?

So, how do I correct a fake 25 fps (it is actually 23,976) into a real 25 fps?

[DB83]

I do not think you have this right.

Yes. Standard PAL used 'Speed-up' so the running time was 96% of film. This concurs with the timing >> 96% of 81 = 77


However, more recent transfers with various techniques such as field-blending can result in the original speed. The transfer is still PAL @ 25 fps

[ridibunda]

I compared the two videos. The only difference between them is the extra 15 seconds of credits (at the beginning).

Both HD stream and DVD version includes %100 of the film. Not %96.

If that transfer was really 25 FPS, the duration would be exactly 01:17:40 (by adding the 15 seconds of new opening credits)

If that transfer was really 25 FPS, the audio track demuxed from PAL DVD could be easily synched with HD video.

Guess what? I synched the audio after I converted it to 23,976 FPS! (audio FPS conversion, HD video untouched)

It sounds weird, but it is true. An audio converted to 23,976 FPS synched with a "fake 25 FPS" video, which is 23,976 FPS actually.

[DB83]

You mis-understand me.

I was NOT saying that the PAL dvd was 96% of the total but it runs slightly faster than a NTSC version. The term is 'PAL-speedup'. Look it up if you do not understand. Or accept that 25 fps would run at 4% faster than 24fps (23.976)


But PAL transfers have enhanced since the early days. You can get a PAL dvd of a film running 77 mins and the same film on PAL dvd running at 81 mins. Both are complete. I know since I have some.


Audio does not have a frame rate just a sampling based on run-length.


I can not add any more. Maybe someone else will contribute.

[ridibunda]

But PAL transfers have enhanced since the early days. You can get a PAL dvd of a film running 77 mins and the same film on PAL dvd running at 81 mins. Both are complete. I know since I have some.

I wrote the calculation above. In each case, the number of total frames has to match with the other.

PAL and NTSC have different durations (because of different frame rates, speeds), but they have the same total frame number. I also wrote where those extra 400 frames came from.

Show me two DVDs (of the same version of a specific film) with the same video framerate, and I'll do a search about them.

PAL transfers enhanced? The film I talk about is made in Europe, it is PAL already. So, why need an "enhanced PAL transfer"?

I haven't seen/heard any DVD/bluray with two different durations in the same region (meaning "same frame rates"). Durations change when you change the region, if you move to USA, Canada or Japan. Or if the film is modified by filmmakers (extended cut, unrated cut, alternative version, etc...)

I think, in your case, your 77 min-PAL DVD must be "theatrical version", 81 min-PAL DVD must be "director's cut". Or the shorter one is "rated" with 4 minutes being cut. There is no other possibility. I know that many DVDs in UK are cut, censored.

I am sure I have a "fake-25 FPS" video, and just wondering why it is like that.

[DB83]

What your calculation proves is the speed-up effect of PAL dvd compared with film. Maybe I confused you when I wrote 'film' meaning the original source medium rather than what you see on the screen now.

I offer you a media info report of two versions of the same film - Munchhausen 1943. On the left is the NTSC version. On the right is the PAL version. You will note that the running time of both is 110 minutes. These dvds are almost 20 years old. It had been re-released but only in Germany and with there being several slightly different versions now in existence it is not so easy to compare.


BTW FPS can not be 'faked'. It has to be stated in the video header to ensure that the media plays at the correct speed.

[Cornucopia]

As DB83 mentioned, many (most?) Film-originated (or now digital cinema-orginated) productions, which are by far most often shot at 24FPS, are pulled down to 23.976 and then Telecined (2:3 cadence) to 29.97 in the case of NTSC, or are pulled up to 25 (with accompanying audio adjustment) in the case of PAL. In either case, there is no blending of frames. In the case of PAL, there is also no adding of frames. If going to an interlace medium, a progressive frame is segmented for PAL, and more finely Telecined and segmented for NTSC. In all of those cases, the number of true original frames (not counting those added to the cadence in the NTSC Telecine case) is IDENTICAL to the original, but the overall runtime will change due to the duration of each frame (= 1/FPS). Very slightly longer (0.1%) in the case of NTSC, and ~4% shorter in the case of PAL. Those new framerates are not "FAKED" at all, however. They just aren't the original framerates. And, in both cases, one can losslessly return back to the orignal 24FPS if desired, by using an inverse process

As DB83 mentioned, there are also newer methods which don't use speedup/slowdown, but which instead use blending in order to maintain the exact runtime, but which don't have much of the original frames anymore because of the blending/interpolation. Reversing the process is NOT lossless, due to the blending.

And there are also Video-originated productions which could be 24, 25, 23.976, 30, etc. Those each have preferred and non-preferred methods of adjustment.

@ridibunda, your film follows the 1st example, with the exception that it has those additional 400 opening title frames inserted. THIS IS NORMAL (not counting the 400 frames). The DVD medium was not designed to accommodate the original (Film/DigiCine) framerate, only Video framerates common at the time, so this was necessary. And the DVD spec has not been changed since. The BD spec WAS designed to accommodate true 24FPS framerate, so it is easier now with Blurays to just have the production company do a straight transfer of 24FPS or of pulled down 23.976, and let the player do the realtime conversion to the video format of choice or of necessity based on the playback equipment.


Scott

[manono]

How about a couple of samples? 10 seconds or so of a scene with steady motion.

As I hope has been made clear by now, much of what ridibunda writes is uninformed nonsense.

[ridibunda]

@manono I am just writing my experiences. If you don't have an answer with a little bit of info, don't join the thread, so simple.

Two videos: One is PAL DVD, the other one is HD remaster... They both are reported&played as 25 fps, but their playback speeds are really different. Even after 10 seconds, they are not at the same scene, at the same point. That is a prove of different frame rates per second. Total duration is different already.

I still couldn't get a clear answer for those simple questions:

- Why is the 25 fps PAL DVD-sourced audio track is unsynchronised with that "seen as 25-FPS" video (which I call "fake-25 FPS")?

- Why did it become synchronised with the video, after slowing down the audio to 23,976 fps?

- Isn't it possible that new transfer is done in 23,976 fps, but released as 25 fps, in order to be compatible with Europe's standard?


I have another "seen-as-25 FPS" video, which I managed to synch with PAL-DVD audio, after converting the audio to 24 FPS. That makes me think that HD remastering was done as 24 fps.

I am not surprised to see such 23,976 or 24 fps remasterings, %99 of bluray remasterings are like this already. It is hard to find 25 fps bluray releases.

I just find it confusing why they are "faked" as 25 fps. I insist on the term "faking", because of my "synch experiences". For some members, they might be "nonsense".

Changing audio track speed (a.k.a. "audio FPS conversion"):


[Attachment 63565 - Click to enlarge]

Let me inform you that real-25-FPS HD videos are easily synched with PAL DVD-sourced audios. With a few seconds of delay value, or a few seconds being cut. No conversions. No slowing-down or speeding-up.

You will ask "What's your point?". The answer is "to get the highest quality". Generally, there are 5.1 sounds on DVD and only 2.0 sounds on HD streams. So, where you have a 6 ch sound, why would you prefer stereo? So simple.

If you don't do any audio-video synch, if you don't chase the highest video-audio quality possible, just ignore the thread.

I opened this thread to understand a few videos which I find "extraordinary".

[DB83]

Sorry. But if you can not get your head around the basic concept of PAL speed-up then we are just wasting our time.

[manono]

If you don't have an answer with a little bit of info, don't join the thread, so simple..

I asked for samples so we could study your sources. "so simple.." Yet you refuse to do even that and would rather continue spouting nonsense, like this:

...(which I call "fake-25 FPS")?

[DB83]

And for clarity, no one suggests that a 77 min vid will sync (as in play at the same time) as a 81 min one)

The purpose of the samples is to establish the technique in the creation of the 81 min one (not that there is much doubt in my humble opinion)