HD-SDI not 1080P?

basspig

basspig

Veteran
I was doing some research on HD-SDI when I stopped across this Wikipedia page: http://en.wikipedia.org/wiki/Serial_digital_interface

Specifically:
SMPTE 292MHD-SDI1.485 Gbit/s, and 1.485/1.001 Gbit/s720p, 1080i

I thought the HD-SDI output of the EX series was supposed to be 1080P. From this article, the only interface that supports progressive is Dual-Link HD-SDI. Is that what the EX have, or is the SDI really just 1080i after all?

From my experience with interlaced output, much vertical resolution is lost, as is chroma resolution, so it may actually be better quality to record to SxS than use the SDI output, if it is only 1080i.

Can anyone confirm whether it's really Dual-Link HD-SDI and real 1080p, or just HDV quality output (interlaced with phony 3:2 pulldown)?
 
If you record at 1080x24p, it gets converted to 1080x60i with no vertical resolution loss. Sony calls it PSF I believe. Most HD/SDI capture cards, and the nanoflash, know how to do 3:2 pulldown and convert back to 24p using their capture software.
 
HD-SDI (single link, 15Gbps) can carry the following formats:
720/60p
720/50p
1080/60i
1080/50i
1080/30p (carried losslessly as 60i)
1080/25p (carried losslessly as 50i)
1080/24psf (carried losslessly in 60i)


For the magical 1080/60p and 1080/50p, you need to double the datarate to 3Gbps. And that need either "Dual link HD-SDI" which uses 2 cables or "3G HD-SDI" (AKA simply "3G") (guess what that stands for?).

- Mikko
 
mikkowilson said:
HD-SDI (single link, 15Gbps) can carry the following formats:
720/60p
720/50p
1080/60i
1080/50i
1080/30p (carried losslessly as 60i)
1080/25p (carried losslessly as 50i)
1080/24psf (carried losslessly in 60i)
Click to expand...
Should not the above read as:

1080/30psf (carried losslessly as 60i)
1080/25psf (carried losslessly as 50i)
1080/24p (carried losslessly in 60i)

?

Are you saying that HD-SDI does not support 48Hz for 24PsF? From what I read elsewhere, 24PsF is supported for HD-SDI as one of the legitimate Rec.709 formats. In particular, the Sony EX feeds 24PsF over HD-SDI starting from... um... firmware version 1.11. So the above should, I believe, look like this:

1080/30psf (carried losslessly as 60i)
1080/25psf (carried losslessly as 50i)
1080/24p (carried losslessly in 60i) (default for most cameras)
1080/24psf (carried losslessly in 48i) (available on some cameras)

Basspig, technically on the transport level PsF is still interlaced, and will be recognized as such unless there are flags in the stream and the receiving end cares to read the flags.

basspig said:
or just HDV quality output (interlaced with phony 3:2 pulldown)?
Click to expand...
AFAIK, Canon and Sony HDV cameras indeed output 2-3 pulldown through HD-SDI, but output through FireWire is proper progressive.
 
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If you have all the exact variations from an accurate list Cranky, then it's probably right.

Mine is just a basic list of the possible basic formats from memory. I can't recall all the variations of transport protocol off the top of my head though.

- Mikko
 
I'm concerned about loss of chroma resolution, because when I convert a 30p stream to 60i, the colors turn all blocky and it looks just as bad as HDV. I'm really disappointed that the SDI output is not truely progressive. All the PsF hocus pocus leaves too much room for destruction of the chroma information in the process.
 
THis is the first I've heard that the SDI connection can't do progressive. Is this confirmed by others?
 
It *IS* progressive, just carried in an "interlaced" stream.

The data is chopped up, and the packets are simply sent slightly out of order. On the other end they are re-assembled back into the right order. There is no magic or voodoo at work, that's simply how digital video works.

You could chop up the data chunks, put some on P2 cards, some on SD cards, some on floppy discs, and take them all to the opposite ends of the earth, then send them back by manual telegraph, re-assemble them into the right order, and it would still be an identical signal.


There is no loss of chroma, or other, data when carrying a progressive signal in a HD-SDI stream.
Just the same as there is no loss when recording 24P footage in an interlaced DVCPRO-HD (or even DV) stream.


- Mkiok
 
According to the Wikipedia article, only Dual-link HD-SDI can carry a 1080P signal.

I remain skeptical about the loss of chroma resolution. I see it in HDV, where the 24/30P is embedded in a 60i stream and the color is about half the resolution. I also see it when I convert 30P XDCam footage to a 60i version for Blu-ray. Color loses half the vertical resolution.

Theoretically, it should be possible to embedd without losing anything, but in practice, it doesn't always work out that way.
 
basspig said:
According to the Wikipedia article, only Dual-link HD-SDI can carry a 1080P signal.

I remain skeptical about the loss of chroma resolution. I see it in HDV, where the 24/30P is embedded in a 60i stream and the color is about half the resolution. I also see it when I convert 30P XDCam footage to a 60i version for Blu-ray. Color loses half the vertical resolution.

Theoretically, it should be possible to embedd without losing anything, but in practice, it doesn't always work out that way.
Click to expand...

Basspig, how are knowing the color is 1/2 the vertical resolution?

This sounds like an NLE issue with the conversion from 30p to 60i, not an SDI aquisition issue.
 
You might be right about that. In that case, it's also a problem with HDV, because both HDV and XDCam that's been converted to 60i have those blocky reds.

I have long suspected that Clip Browser, when converting XDCam to MXF for NLE, converts to interlaced as well, because I have been unable to use any of the MXF clips because of the jaggies and the blocky color. It loses the photorealism and gets that HDV look. Perhaps that is an Adobe Premiere/MainConcept problem, but it does suggest that interlaced footage has a much higher probability of being screwed up than purely progressive footage.
 
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