PAL DVD plackback at 48i/24p?

[daveloc]

It's well known that most PAL DVDs created from 24fps film source effectively play back 4% faster than the original cinema presentation, at (50Hz=50i=25p), with the sound a fraction of a tone high.

Now we have 24p-native TVs, is there any reason that BD/upscaling DVD players couldn't offer the option to play such DVDs at the "correct" 48Hz (i.e., same as BluRay's 1080/24p after upscaling and reinterlacing) — it looks to me like a straight clocking issue, and since the disc read speed would be lower rather than higher, wouldn't hit any limits there.

It has to be an option, of course, because not all PAL DVDs are from 24fps source. As a side-benefit, it should cure the 50Hz motion artifacts seen on some 24p TVs/BD players in the last couple of years.

Anyone at WHF ever heard of, or asked manufacturers about, this?

 

[aliEnRIK]

Ive got a few NTSC dvds that play at 24Hz. My Sony S370 plays them no problem

 

[landzw]

Could someone enlighten me as this does a bit harsh or rude but truthfully why are we worrying about 24 fps or 25 fps surely our eyes can't see the difference , surely its just a marketing deploy

 

[aliEnRIK]

landzw:Could someone enlighten me as this does a bit harsh or rude but truthfully why are we worrying about 24 fps or 25 fps surely our eyes can't see the difference , surely its just a marketing deploy

Movies are recorded at 24Hz (Far too slow for this day and age so far as im concerned)

Playing back at 25Hz (Technically 50Hz), as explaned above, speeds up the sound. Playing back at the true 24Hz retains everything as it should be seen and heard

No marketing ploy involved

Things get a lot more complicated with 50Hz and 60Hz material, as you then get 'pulldown' problems etc. But thats another matter

 

[landzw]

So is the film slightly longer in 24fps ?

 

[robjcooper]

Yes it will indeed be longer - 4% longer in fact.

And the reason that you can't play DVD's at 24 fps is that they are not mastered at that frame rate. Most feature films available in standard def will have been played from a telecine at 25fps rather than 24fps onto Digi Beta Tape (which for UK use only record at 25fps) and all those TV shows will be on 25 frame master tapes. Anything released in the UK as region 2 will have originated from these tapes and been encoded to MPEG2 for DVD. MPEG2 does not contain discrete frame information so the mpeg data stream would have to be unpacked back into discrete frames and then the frame playback altered from there. However more fundamentally, the internationally agreed spec for DVD only allows for 25 (PAL) or 29.97 (NTSC) frame rates, so really the argument is purely academic and when the DVD spec was ratified there were no TVs capable of playing back at 24fps either. Material mastered onto HD at 24fps will have also been gear shifted to 25 frames if used for DVD release. Obviously, 50i HD material runs at 25 fps so needs no tinkering.

If you fancy a good technical read about mpeg2 compression, i would recommend:

http://www.bbc.co.uk/rd/pubs/papers/paper_14/paper_14.shtml

Rob