BBC: DVD Region coding system on the verge of colapse! (1 Viewer)

[DaViD Boulet]

How a DVD player converts a "film" source (24 fps native) PAL DVD (which has been "sped up" so that it's displaying 25 fps) to NTSC can take several approaches and who know's what's really going on.

The best approach would be for the DVD player, knowing that it is going to be producing an NTSC or 480P image, to "slow down" the audio and discard the repeated 25th frame...then output the signal as a conventional 480P image by applying 3-2 pulldown to up you to 30 frames-per-second (progressive scan).

However, the same DVD player outputing a PAL signal would have to leave the speedup for the PAL TV sets which need that 25 frames/50 fields per second.

Anyone know if the conversion players like the Malata compensate for the speedup when outputing PAL-encoded film source material in NTSC or 480P?

-dave

 

[CamiloCamacho]

I don't support region coding. I'm a proud owner of a region free deck and I get what I want, when I want, from where I want

I totally agree with you. I think a "Future" release will make a lot of DTS entusiasts potential buyers of a DVD Region Free Player.

 

[Ted Todorov]

The best approach would be for the DVD player, knowing that it is going to be producing an NTSC or 480P image, to "slow down" the audio and discard the repeated 25th frame...

The whole point is that there is no repeated 25th frame. From what I know, for a PAL transfer the film is run at 25fps during the telecine process. It then resides on the PAL DVD with no added frames compared to the original film print, but a 4% shorter running time vs. 24fps projection or an NTSC DVD transfer.

Ted

 

[DaViD Boulet]

Ted, you're right. My bad!

Ok...so scrap the line about the repeated frame. But the point is that I'm wondering if the PAL-NTSC conversion in the dvd player has built into the process *slowing down* the audio/video and outputting this signal as a 24 fps image that then gets 3/2 applied for 30 field/frame 480I/P playback.

This would make the most sense...and it seems it would not be hard to do. I mean hey...my minidisc player can adjust pitch and speed...so why not a DVD player?

-dave

 

[stephen abbot]

This whole matter is off topic, but I would like to explain roughly what happens.

When a film is coded to disc, it occurs at 24fps. When 50Hz country player plays it out it speeds up the playout to 25Hz with a 2:2 (or 1:1 depending on how pedantic you are) interlace frame rate. The audio is also clocked thru the DD decoder at a 4% higher rate to match. When a 60Hz country player plays this out (and this includes "converting" players such as the malata) the video undergoes the same 3:2 pulldown process that is required to transfer 24fps to 30fps, the audio is clocked out with no speedup. This play out is identical to if the disc was a 60Hz (NTSC) coded disc, the only difference being the need to perform a spatial reduction of 720x576 o 720x480.

When 50Hz (PAL) video material is coded to disc, it does so at 25fps, the audio essentially is coded at normal rate. When played back on a 50Hz system the video and audio clock out as they were clocked in, therefore no speedup is experienced.
I may be mistaken but I understand that if the disc was played out on a converting player the machine must repeat frames at an appropriate rate to effect a 25 > 30fps increase. The audio however is still played out at the same rate, so no speedup is experienced. It is the repeating of frames that causes unnatural motion (temporal) effects that is disturbing, a good broadcast converter will infact interpolate frames rather than repeating them. I understand that converting players do not do this, they simply repeat frames. Obviously the same spatial scaling reduction is required as for film sources.
Note, the requirement for 3:2 pulldown is not used as this would create a similar temporal judder that 3:2 pulldown creates and reduce speed by 4% a double negative.

Regards

Stephen