Puzzled over DivX/704x396/120fps... Why?

[ssme80386]

From time to time someone at zero-raws releases files spec.ed: DivX(?) 704x396(?!) 120fps(?!!) 250+MB(??).

I can understand divx+400lines - for ancient pcs, but the rest of the specs speaks against such hypothesis..

Can anyone enlighten me what would be the purpose of such exercise? Does anyone download them?

[Tofusensei]

Hi. 120fps raws have been around for ages. Japanese cappers started using them and they caught on because they let you handle hybrid material relatively easily.

The answer is they are not actually 120fps. They are filled with dropped frames so it's not as bad on playback as you would think.

The file you described should play on a mid-level P4 with no issue.

[jfs]

And for the record, there are tools that let you convert them to proper VFR. If you just make an MKV straight from the file you get a proper VFR file with no additional work, and if you use eg. FFmpegSource2 in Avisynth for re-encoding the file you can get a VFR timecode file for it as well.

[ssme80386]

I see...

I understand why 120fps is convenient if you use video EQUIPMENT limited by tv signal nature - if it's NTSC - you have to produce 29.97fps, etc., but why would you you need it on a computer?

For a software player fps is just another parameter, like resolution. If the source is 24fps - make 24fps file - it would be played at 24fps, if it's 30fps - it would be played at 30fps, if it's european source - here you are - 25fps...

Why had it even started for PC video files? What don't I understand?

[Quarkboy]

Smart people are not explaining properly, so let me fill in the gaps.

Most anime is actually hybrid between 24 frames per second and 30 frames per second.

In order to have a constant frame rate video that has all the frames at the correct times, you have to have a video with a frame rate = least common multiple of 24 and 30 = 120.

i.e. during the 24 fps sections every 5th frame is new, and during the 30 fps sections every 4th frame is new, with the rest duplicates (i.e. dropped frames).

[ssme80386]

Wait a second!

Most anime is actually a TV broadcast in Japan. Which is NTSC. Which is 30fps period. I have never heard about variable fps NTSC TV signals - if that's what you mean by hybrid...

Is it not so?

[ssme80386]

Ah! yeah, right.....

the file in question is rip from satellite broadcaster, yes, they use i60 to be able to mix 24fps and 30fps material in the same mpeg2 stream using metadata.... (but they still need only 60fps!)

I agree, hybrid TV source is technically feasible (today! not "ages ago"!) - and if you say it IS hybrid I buy it at face value (how do you know?)...

Still it all seems to be over-complicated... Starting with: why the hell would the authors of an anime create it as hybrid source?! I understand if a TV station mixes DIFFERENT programs - some 30fps, others 24fps - in the same channel-stream, but within the same program... ads? the ads are to be cut out anyway...

puzzles... puzzles...

[crash-kun]

im pretty sure that all NTSC ever is/was 60 fields per sec, ie 30 frames per sec

[Quarkboy]

Originally Posted by ssme80386

Still it all seems to be over-complicated... Starting with: why the hell would the authors of an anime create it as hybrid source?! I understand if a TV station mixes DIFFERENT programs - some 30fps, others 24fps - in the same channel-stream, but within the same program... ads? the ads are to be cut out anyway...

puzzles... puzzles...

The reason anime is created in a hybrid way has a long and tangled history, but basically it comes down to this:

animation is traditionally done at 24 fps because it started with film. Also, 24 is 2*2*2*3 which means it has more divisors than 30=2*3*5, which makes doing limited animation easier.

But when anime is on TV it started using more NTSC, i.e. 30 fps equipment for editing and compositing. Now that everything is digital, digital equipment might do the final editing for fades/pans, etc at 30 fps for a TV anime. Some opening and endings have been natively animated in 30 fps because it provides smoother motion. CG effects can be rendered in any framerate, and they are often done at 30 fps for TV anime.

So while many anime are still done 100% 24 fps progressive, a lot are also a hybrid of 30 and 24.

[ssme80386]

Thanks for the explanation, Quarkboy.

[TheFluff]

Originally Posted by ssme80386

Wait a second!

Most anime is actually a TV broadcast in Japan. Which is NTSC. Which is 30fps period. I have never heard about variable fps NTSC TV signals - if that's what you mean by hybrid...

Is it not so?

they're strictly speaking not variable FPS, it's a mix of 24fps telecined to 30fps and actual 30fps content

[Nicholi]

Originally Posted by Quarkboy

Smart people are not explaining properly, so let me fill in the gaps.

Most anime is actually hybrid between 24 frames per second and 30 frames per second.

In order to have a constant frame rate video that has all the frames at the correct times, you have to have a video with a frame rate = least common multiple of 24 and 30 = 120.

i.e. during the 24 fps sections every 5th frame is new, and during the 30 fps sections every 4th frame is new, with the rest duplicates (i.e. dropped frames).

You forgot to mention the only reason "we" need the framerate to be constant here in PC-land is because of AVI. Otherwise 120fps is useless with real containers.

[Emess]

But Nicholi, nobody needs AVI anymore, not unless they have an ancient old Athlon64 or worse...

E~

[D404]

Originally Posted by Emess

But Nicholi, nobody needs AVI anymore, not unless they have an ancient old Athlon64 or worse...

E~

I'm not sure if this was supposed to be a clever troll or just Emess failing...