60 VS 59.94 and 24 VS 23.98

[silikone]

What is the rule for using fractional frame rates across different mediums? TV is of course fractional in North America, but this raises the question. Since everyone would watch feature films at 23.98 FPS, have they been natively recorded at this frame rate, or are they truly 24 FPS with an imperceivable slowdown applied later? Do Blu-ray movies play at 24 or 23.98?
As for '60 FPS', is this always 59.94, or do real 60Hz signals exist? I always wondered about both 59Hz and 60Hz showing up as display modes on computers, so am I wrong to assume the former actually means 59.94?

[sneaker]

Blu-Ray supports both 23.98 fps as well as 24.0 fps. You will have a hard time finding the latter in the US but you will see it in Europe occasionally. Cinema movies have been produced in 24.0 fps mostly.

"60 Hz" usually refers to the 59.94 variant when talking about movies but the new UltraHD BluRay actually also adds a real 60.0 Hz mode.

[Cornucopia]

My semi-short summary answer:

FILM -
Movie theatres ONLY show things at 24fps (or 48fps for "high" framerate), since the introduction of sound - ignoring the obvious tricks with double- or triple-flashing, the additional requirements of stereo3d projection, and the few rare specialty theatres using Showscan, etc.
So every movie shot for theatres is OPTIMALLY recorded at 24fps. Doesn't mean you can't shoot other ways. But the tools are built with that in mind.
VIDEO (NTSC-based) -
30fps Black & White video (creating 60 fields/second) worked because it was built to be in sync with electrical power cycles (other framerates would have introduced "hum"-bars).
In order to make Color signal fit into the spectrum & format already created for B&W, they slowed down the framerate by 1000/1001 (mainly because tube-based equipment has some play to it and can allow that much deviation without screwing up).
So 30fps (or 60 fields/sec) became 29.97fps (or 59.94 fields/sec).

Whenever showing 24fps on B&W video, pulldown was applied in a 2:3:2:3 repeating pattern to arrive at the exact 30fps. Applying the same slowdown to 24fps-originated footage allows 23.976 material to be "pulled-down" to 29.97.

Digital started by just mimicking the analog world it was born from. But now it allows easier conversions & shortcuts, as well as not being tied down to things like electrical powerline frequency.

So now, movies shot at 24fps are later applied a slowdown to 23.976 to be put that way on BD, or if they want they can leave it at 24fps and just let the player generate the slowdown to 23.976 (if going to DVD, they're almost always pulled-down - soft or hard - to 29.97). Then it will have to apply the pulldown in playback to get it to 29.97/59.94 (because most NTSC-type TSs still operate at that display refresh rate).

There are some who actually KNOW that they aren't going to ever get shown in the theatres, but still want their style to be film-style (using 24fps and shallow focus, etc). And those people CAN decide to shoot directly at 23.976. But they have to be careful about audio sync (yes, there are tools that apply similar slowdown with audio samplerates, from 48kHz to 47.952kHz, etc).

Since nobody actually has broadcast true B&W ntsc for a while (and even the few closed-circuit B&W security systems have all but disappeared), there hasn't been a true 30fps (60 field/sec) use for a while...until the Internet, where non-technical video enthusiasts have made it popular. And since many computer monitors (unlike consumer TVs) can and do operate at exactly 60Hz display refresh, this makes things easier for them (but complicates things for the analog-video-originated folks).

"59Hz" does usually mean 59.94Hz, but not necessarily (as many monitors can have even more display refresh rate choices).

Does that answer your question?

Scott

[flashandpan007]

the new UltraHD BluRay actually also adds a real 60.0 Hz mode.

Do you have a source that it supports 60.000fps? I can't believe that

[flashandpan007]

"59Hz" does usually mean 59.94Hz, but not necessarily (as many monitors can have even more display refresh rate choices)

I only know about 59Hz is 59.94 (exactly 60/1.001) What else can it be?

[silikone]

Does that answer your question?

Sure.
I am however now in conflict between rooting for 60 or 59.94. If I use the former on my screen, I will ensure that no frames get skipped whatever the content, but I will in theory get double frames for everything from the television world.
Maybe it doesn't matter. In the end, they are both silky smooth.

[hello_hello]

I've wondered if hardware players tend to adjust the playback rate a tad to make up for refresh rate differences but it's not something I can test.

If you use a PC for playback, you can always use Reclock. It'll adjust the frame rate a little to match the refresh rate. I live in PAL-land and being lazy I just leave my TV refreshing at 50Hz and use Reclock to watch everything at 25fps (except 29.97 progressive or 59.94 interlaced video, but I don't have much of that).

According to Reclock this PC (not the one I use for video) and my TV are connected at 60.001Hz. From memory 50Hz is really 50.002Hz and 24Hz is slightly less exact.

[sneaker]

the new UltraHD BluRay actually also adds a real 60.0 Hz mode.

Do you have a source that it supports 60.000fps? I can't believe that

It's listed in various tables in the following paper coming from the Blu-ray Disc Association:
http://www.blu-raydisc.com/Assets/Downloadablefile/BD-ROM-AV-WhitePaper_HEVC_150608a-clean.pdf

[flashandpan007]

Nice

[hello_hello]

Does that pdf only describe the new specification? I asked, because i see no mention of SD or DVD support. Or 720p for that matter. Does it mean the minimum supported reolution for UHD Bluray players will be 1080p?

[sneaker]

It only describes HEVC coding. At least 1080p AVC will also be supported. I do not know whether 720p and SD are allowed to be mixed in on UltraHD BluRay, i.e. whether this is only an extension to existing Blu-Ray or if UltraHD does away with them entirely. (backwards compatibility of UHD BluRay players with old BluRays notwithstanding)

[silikone]

http://www.blu-raydisc.com/Assets/Downloadablefile/BD-ROM-AV-WhitePaper_HEVC_150608a-clean.pdf

No 30?

[pandy]

What is the rule for using fractional frame rates across different mediums? TV is of course fractional in North America, but this raises the question. Since everyone would watch feature films at 23.98 FPS, have they been natively recorded at this frame rate, or are they truly 24 FPS with an imperceivable slowdown applied later? Do Blu-ray movies play at 24 or 23.98?
As for '60 FPS', is this always 59.94, or do real 60Hz signals exist? I always wondered about both 59Hz and 60Hz showing up as display modes on computers, so am I wrong to assume the former actually means 59.94?

Rule is simple - if your goal is to use NTSC color encoding (at some point of your HW configuration you will use NTSC composite signal) then you must use 60000/1001 rate. If NTSC composite is not your goal then you are fine to not use fractional frame rates.

Side to second part - there are subtle differences between fractional and non fractional modes but digital video interfaces such as DVI or HDMI have no separate signalization for fractional and not fractional framerates (so called Short Video Descriptor is shared by fractional and non fractional video mode - difference is signaled trough different pixel clock).

[silikone]

Side to second part - there are subtle differences between fractional and non fractional modes but digital video interfaces such as DVI or HDMI have no separate signalization for fractional and not fractional framerates (so called Short Video Descriptor is shared by fractional and non fractional video mode - difference is signaled trough different pixel clock).

Very interesting. Is there a way to see the exact pixel clock and do the math from there?

[pandy]

Well - DVI and HDMI use pixel clock so you are able to measure frequency and based on this perform all math - check CEA/EIA-861 - everything is there.