1394 4:2:2 ?
 

Can the JVC do this? I've been doing research on trying to get the camera modified for complete 4:4:4, but that's not gonna happen. I came along Adam Wilt's page and saw that firewire should output this, if it doesn't on the JVC, can I ask...why not?

http://www.adamwilt.com/DV-FAQ-tech.html#1394

Not via the 1394, only by the component out can you get 4:2:2. And no support for 4:4:4 unless you upsample, and even then I don't believe you gain anything.

exactly what i figured, my question is why? if the output is better via firewire(in the article) then why is it out analog and not firewire for the JVC?

It's a simple matter of the technical specifications of HDV. You can't do 4:2:2 over Firewire because HDV isn't 4:2:2.

Best way to get high quality 4:2:2 out of the camera would be getting the HD250 with its SDI out and capturing using an external capture solution that will accept SDI.

From my limited understanding I believe that the tape transport and mini DV tapes/speed would not support an uncompressed 4:2:2 signal, in simple terms too large a data rate. Same goes for Firewire and HD uncompressed, you need a larger pipe for HD than firewire can support. So although the 1394 is a sufficient path after encoding of HDV (being that the data rate is reduced) it's not going to support 30-60P HD. The component out is simply putting out a series of images, you still need something to capture like the Decklink or Kona, the datarate of firewire does not even cut it here. That is unless you are cool with being limited to less overhead like maybe 24P.

4:2:2 does not mean uncompressed. Any codec can be 4:2:2 so data rate isn't the factor. HDV is a recorded to tape format that happens to be 4:2:0. Firewire is nothing other than a transfer device, and can handle vast amounts of data over what HDV uses, then there is firewire 800 at twice that data rate if anyone in the industry wanted to implement it. Firewire moves data from one device to another. Just like if you had a firewire hard drive plugged into your computer. If HDV was designed to be 4:2:2 or 4:4:4 then firewire would transfer that, but HDV is 4:2:0. End of story. Thats what the cam captures and that is what firewire transfers. If you want to get away from any cams compression format (HDV, DVCproHD, HDcam ect..) you have to output HDMI, Component, or SDI.

I don't think you'll see 4:4:4 coming over any firewire connection unless it's ultra-low resolution. Especially not 1394a with its 400 mbs data rate. 1080i 60 uncompressed 4:2:2 @ 10bit depth requires over 1 gbs data rate. The equivalent signal at 8 bit depth is just under 1 gbs. Much too fast for even firewire 800 to handle.

-gb-

Uncompressed, yes, but HDV is compressed to less than 19.7 Mbits/sec, well within the limits of the Firewire specification, it's not too much of a stretch to say that with similar coding techniques you could easily fit 4:2:2 or even 4:4:4 on a Firewire link. It's just a matter of having a tape format that can handle the data rate, and little details like having an actual codec to do it for you =D Take a look at HDCAM SR, it's an intraframe compressed tape format that fits a 1920x1080 60i 4:4:4 RGB stream into 440 Mbits/sec. Internally the codec is MPEG-4 studio profile (HDV is MPEG-2). It would be possible to stream HDCAM SR over a Firewire 800 link. Too bad the decks cost more than your house and the tapes are bigger than the HD100. =D

The tapes are also the limit.

DVCPROHD runs at 100 mbits and can be sent over normal firewire with great ease. Sadly mini DV tapes cannot run that fast without ripping to shreds or having dropouts all over the place. HDV was meant for us to be able to use cheap DV tapes to keep the cost down. Normal HDCAM is only 144 mbits which would be small enough to fit over firewire no problem at all but sadly I do not see that option ever coming to us. In order for a DV tape to fit that level of bandwidth it would have to run almost 6 times as fast. A tape that thin could never handle that.

It sure would be nice if HDV cameras could encode at a higher bitrate when sending the signal live to a NLE. The max limit for mpeg-2 is 300 mbits which should fit over a 400 mbit firewire connection. I doubt we will ever see this however. 300 mbit I frame only 4:2:2 mpeg-2 is pretty darn good and very close to uncompressed in terms of visual quality. The Matrox Axio system this level of mpeg-2 encoding for it's live uncompressed systems. I have also been working on a live capture encoder for those with uncompressed capture cards but I am pretty sure you will need a 4 cpu system in order to capture at that level.

With that said I have played around with 50 mbit IPB 4:2:2 HD and it looks pretty darn good. That is twice the rate of HDV and it really helps. I did some test HD footage shaking and wipping a camera all over my office and it held together pretty well when I encoded the uncompressed file to the 50 mbit version.

Part of the method used for getting HDV and other formats to that datarate is to use chroma subsampling along with compression. But you absolutely can fit more data than this on a fw connection. As mentioned, DVCPROHD at 100 mbs can transfer over firewire. But 4:4:4 using

Not quite. HDCAM SR runs in two flavors. It's only 4:4:4 in RGB mode when using dual channel HDSDI into a disk array. When going to tape, it runs in YUV mode and is 4:2:2.

I believe the 440 mbs rate you referenced is for regular HDCAM which is 1440X1080 and 3:1:1 subsampling.

-gb-

regular HDCAM is only 144 mbits.

Yeah that's right, Thomas. I keep getting uncompressed data rates mixed into my brain. I have a slide from a presentation that shows uncompressed data rates for 1080 video at various frame rates and bit depths.

Mea culpa,

-gb-

This page was my reference for the data on HDCAM SR.

I eventually went and looked in the FCP manual which also has the numbers you referenced. HDCAM SR 10 bit 4:4:4 can go to tape compressed to 440 mbs, but it gets more compression(4.2:1) vs. the 4:2:2 (2.7:1). So you sacrifice one or the other to get down to 440 on tape.

As I mentioned to Thomas, I was originally referencing a chart comparing uncompressed 1080 data rates.

I humbly apologize for the misinformation.

-gb-

edit: I think the other part of the confusion is discussing megabytes/sec vs. megabits/sec. I was quoting the latter which is much higher than the former.

Matt if your interested in 4:4:4 from prosumer cameras
check out reel-stream.com (they have modded a dvx100 to do HD and they may do the HD100 in the future)