Pulldown flags, 24p vs. 30i

[vlada]

Hello,

I have one theoretical question. There's one thing I don't fully understand about telecine and pulldown flags. I'll explain you my theory and please tell me, what's wrong with it.

From the explanations about pulldown flags I've read, it tells the decoder how to combine fields from progressively encoded frames to get 30i output. If the video is really encoded as 24p, why is it a problem to simply ignore the pulldown flags and output 24p? In this case there would be no need for an inverse telecine filter.

But it apparently doesn't work like this. What assumptions in my theory are wrong?

[mellon]

Your considerations are mostly true.

Some clarifications and remarks on terminology: There exist two kinds of 24p. On the one hand there is "true 24p". The video stream exports a constant framerate of 24 progressive frames per second and there is no pulldown flag. This is permitted on Blu-Ray but prohibited on HD DVD (until now).
On the other hand there are video streams exporting a constant framerate of 23.976 progressive frames per second with pulldown flag set. This permitted on Blu-Ray and HD DVD. This is sold as 24p to the customer.

The current HD DVD spec wants the player to apply pulldown on 23.976 fps progressive content. Furthermore the spec prohibits any conversion of 23.976 progressive content to one of the PAL framerates (50Hz system - 25p or 50i or 50p).

You are right. The player has to ignore the pulldown flag on 23.976 content to output nearly 24p.

When you now think Blu-Ray is the better format - don't!
1. Most BD have 23.976 streams on it.
2. If output system is 60Hz the player software must apply pulldown and find itself the best frames for this. This could look even worse because of cheap player software and slow hardware.

Most probably the HD DVD guys update their spec to permit "true 24p".

The problems arise when the hardware player tries to negotiate with the display hardware. And even if one forces the player to output "near 24p" or "true 24p" - display devices might apply pulldown internally.

What's best: fully configurable equipment. In most cases this could be a software player and a beamer or CRT display. I'd like to have a LCD outputting at 72Hz. But I did not find one.

[Leak]

I'd like to have a LCD outputting at 72Hz. But I did not find one.
My crappy old BenQ FP71E+ 1280x1024 17" TFT works from 55 to 75 Hz via DVI, but you also need PowerStrip to set the refresh rate to your liking, as without it all you can select is 60, 70 or 75 Hz...

Too bad you hardly ever get any indication which vertical refresh rates a display supports nowadays, be it in spec sheets or reviews... :(

Samsung's 226BW (http://www.prad.de/new/monitore/test/2007/test-samsung-226bw.html) supports 56-75Hz, according to the spec sheet at Prad.de...

[scarbrtj]

I have not yet come across any VC-1, AVC, or MPEG-2 stream @ 24 fps (they've all been 23.976 fps) on Blu-ray. Any of you guys seen any titles @ 24 fps?

[bmnot]

I have not yet come across any VC-1, AVC, or MPEG-2 stream @ 24 fps (they've all been 23.976 fps) on Blu-ray. Any of you guys seen any titles @ 24 fps?

Yes, but only on Hong Kong movies. Infernal Affairs is one that is exactly 24.000
I think there is another one.

[vlada]

I live in Europe so I don't come across many NTSC DVDs. But I was always wondering why I need to apply inverse telecine filters to get a progressive movie from them. Is it a missing option in ffmpeg, that it can't ignore pulldown flags?

[reepa]

My crappy old BenQ FP71E+ 1280x1024 17" TFT works from 55 to 75 Hz via DVI

I've heard claims that LCD monitors internally convert to 60Hz (although I don't understand why they would do that). This HP L1906 I'm currently using supports up to 75Hz. Ciao.co.uk usually has specs for the max horizontal and refresh rates.

[Leak]

I've heard claims that LCD monitors internally convert to 60Hz (although I don't understand why they would do that).
Well, the POS 20" Acer I also bought a while ago, while not really "converting" the frame rate, works with a fixed internal refresh rate you just can't hit with a graphics card, so depending on the refresh rate supplied by the graphics card you get a few dropped frames per second to a dropped frame every few seconds... :(

But the BenQ syncs perfectly to any refresh rate from 55 to 75 Hz I've thrown at it.

np: Sole & The Skyrider Band - Stupid Things Implode On Themselves (Sole & The Skyrider Band)

[LoRd_MuldeR]

Samsung's 226BW (http://www.prad.de/new/monitore/test/2007/test-samsung-226bw.html) supports 56-75Hz, according to the spec sheet at Prad.de...

I've got the 226cw, and it does support 75 Hz.
But unfortunately not at it's full/native resolution of 1680x1050 :rolleyes:

[Leak]

I've got the 226cw, and it does support 75 Hz.
But unfortunately not at it's full/native resolution of 1680x1050 :rolleyes:
I guess that's not very surprising since that'd exceed the bandwidth of a single link DVI connection... :(