SDI Noob Question

The Nightfly

Active Member
Whats the framerate coming out of an SDI modded player?

I'm just wondering how an SDI player handles R1 DVD. I'm thinking about replacing my HTPC and going the DVD player + scaler route to feed my H79 projector. A big advantage of HTPC is that it can feed the PJ at 48Hz to avoid telecine judder. Is the frame-rate from SDI 23.975Hz/24Hz, or is it locked at 60Hz?

Allan
 

kurtz

Active Member
SDI outputs as close as you can get to what is on the disc, so it will output 576i @ 50Hz for PAL and 480i @ 60Hz for NTSC. This is then fed into a scaler which can do deinterlacing and frame rate conversion for you, doing 3:2 pull down on the NTSC and turning it into 48Hz frames.

Edit: just on my way out the door to Bristol Show, but just a quick note that you could also consider HDMI to a scaler - because some (not all) players can output 480i/576i over HDMI, e.g. Pioneer, Marantz, Arcam plus some cheaper ones.
 

MarkE19

Moderator
As kurtz has said an SDI mod DVD player will output near enough exactly what is on the disc, as the whole point of SDI is that it outputs the video direct from the MPEG decoder and bypasses the processing that is normally done to the video signal within the player. It therefore gives a cleaner signal to the video processor to manipulate and match exactly to the specs of your display.

Mark.
 

The Nightfly

Active Member
Ok, thanks guys. I'm currently contemplating replacing my HTPC setup with a DVD player + scaler combo. If I went the DVD player/scaler route, To fit in budget I'd then be considering the pro's and con's of getting an older, component only, DVD player SDI modified or getting a newer player with interlaced digital output. For example Arcam DV88 with SDI mod vs Arcam DV79

One of the things in favour of the HTPC is that it can play region 1 disks at 48Hz and avoid 3:2 pulldown and associated judder. I'm still a bit confused though. I use a piece of software on the HTPC called reclock to better syncronise the audio and video clocks for smoother playback. If I'm playing a R1 DVD, reclock's information window tells me that the framerate recorded on the disk is 23.975Hz. Reclock then speeds up the playback (audio and video) very slightly to make it exactly 24Hz and because the graphics card is set to 48Hz exactly (using powerstrip on the PC) a simple doubling of the framerate is required and super smooth playback results.

What I believe normally happens in a DVD player playing a R1 disk is that the 3:2 pulldown process is applied to the 23.975Hz framerate to arrive at 60Hz on the DVD players outputs (component, digital or whatever) to make it compatible with a USA TV set. Am I right in thinking that the frame-rate recorded on the disk itself is 23.975Hz rather than 60Hz. The 60Hz is just the result of some processing internally within the DVD player?

So getting back to the original question, if the SDI is outputting 60Hz, does that mean the mpeg decoder is doing the 3:2 pulldown processing?

Allan
 

kurtz

Active Member
Am I right in thinking that the frame-rate recorded on the disk itself is 23.975Hz rather than 60Hz. The 60Hz is just the result of some processing internally within the DVD player?

Yes, sort of. Actually its 59.94Hz (60 fields in 1.001 seconds), which ties in with the 23.975Hz figure your PC is giving. There's a good article on the secrets of home theatre site which describes the process of 3-2 pulldown, and about deinterlacing. I think what you are getting at is described in their "3-2 pulldown" section - do a search for "repeat_first_field". In their first example they describe how the frames would be correctly encoded - with the 'progressive' flag set. They then show various erroneous encodings found on discs which mean that they are not all encoded as 23.975Hz frames. If you read on to the next section "why deinterlacing is necessary" they discuss about not all of the frames being stored progressively.

Then in the next section "Film-Mode deinterlacing" they state
So what the best players do is use a standard MPEG-2 decoder to generate digital interlaced video and then feed that video to a deinterlacing chip
The deinterlacing chip then detects the 3-2 cadence and can perform inverse telecine to produce 47.95Hz progressive.

So perhaps I should rephrase my first answer to "SDI outputs as close to what you can get from the MPEG decoder". And to answer your original question about the SDI frame rate - well, its interlaced so its not really frames: its 480i at 59.94Hz or 576i at 50Hz. You then feed that into a deinterlacing chip in the scaler.
 

Welwynnick

Distinguished Member
DVDs record video in interlaced digital component (YCbCr) format. Nomatter whether the original source is 24, 25, 50 or 60 fields or frames per second, what goes on the disc and comes out of the MPEG decoder (and straight into SDI) is always 50 (PAL, SECAM) or 60 (NTSC) fields per second.

A good scaler will be able to recover the original 24 fps progressive video, and many can output that at 48 fps. The processes performed by HTPCs and DVDs + scalers are pretty much the same. A PC does not avoid 3:2 pull-down with R1 discs. The discs still store the video at 60 fields/sec, and the PC recovers the original cadence and applies pull-down to generate a progressive frame sequence. That sequence will then be decimated to avoid the unwanted repeated frames. That's a very nice solution, but a PC or scaler wil arrive at the same result by the same means.

Just my opinion, Nick
 

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