JVC GYHD100U 1394 output

[Steve Kuh]

I heard that JVC GYHD100U 1394 output only contains 720p 30p. But, if the Motion Filter is engaged under 30p mode, it will insert repeat flags out of 1394 port such that IRD or decoders will be able to display at 60p. Has anyone tried this approach?

[Tim Dashwood]

I've never heard that. As far as I can tell 30P is 30P whether motion smooth is on or not.
I think what you are essentially asking is "is it possible to capture 720P60 onto tape" and the answer would be no.
However, "live" 720P60 capture is possible, and is unaffected by the motion smooth feature.

[Steve Kuh]

I am actually interested in live capture from the 1394 port by converting the 1394 into ASI for RF link back to studio. I think the 720p60p is only available on the component output. But, from the 1394 port, only the 720p30p is available.

I also talked to JVC engineers and they are saying that there is what is known as "60p syntax" mode out of the 1394 port and waiting details about that now. Has anyone heard about the "60p syntax" mode for 1394 port?

[Nate Weaver]

That sounds to me like what the port would output in a 24p situation.

In HDV-24 mode, the 24 frames are embedded in a 60p stream with repeat flags. Of course the 1394 hardware would have to pass along that 60p stream, even though it really isn't 60p from the CCDs. I'd think that could be construed as "60p syntax"...the port is speaking 60p but really isn't carrying 60p info.

[Brian Duke]

Hey it seems yo me that after I have caputured my footage in 24P there are only 22fps in FCP5. Is this correct? or is there something wrong?

[Steve Mullen]

Originally Posted by Steve Kuh

I also talked to JVC engineers and they are saying that there is what is known as "60p syntax" mode out of the 1394 port and waiting details about that now. Has anyone heard about the "60p syntax" mode for 1394 port?

Interesting. I originally believed that both 24P and 30P were sent using "60P syntax." By that I mean 30P had a Repeat Flag after every frame.

This would allow it to work with hardware decoders because the RF would cause the second image to be generated. Software would ignore the RF because it appears none of the software companies took the RF as a serious indication of things to come (24P). Thus, they ignore it.

I even thought the original JVC's used "60p syntax", but we never knew.

I put all this in the book and then decided I might be wrong. That's because when capturing 24P into AIC the RF are clearly recognized -- which is why we get 720p60. If the 30P used RF, I would think we would get also get 720p60.

But, now that you bring this JVC statement up -- I wonder if I was correct and that AIC simply ignores the RF when it is from 30P.

However, the 60P sytax will do you no good as it doesn't do anything but repeat the last frame upon a RF.

David Newman likely knows the answer!

[Steve Kuh]

I have a customer who actually took the GYHD100 1394 output, converted it into ASI using our HDV-1394-to-ASI converter box, and connected the ASI signal into Tandberg TT1280 IRD ASI-Decoder. This IRD supports 720p60. But, the decoded picture showed stutters on its decoded output when displayed onto an HD monitor.

Assuming that the Repeat Flags were being sent out of the 1394 port, it seems to indicate that TT1280 IRD box is not using the RF. This may be an isolated case or an industry wide issue. If the industry has not practiced the RF widely, at least in the DVB world, then why use the RF on the 1394 output at all? I don't see the point.

I also checked the MPEG2 Video standard, ISO 13818-2, there is no mention of the Repeat Flag. This may be the reason that not too many hardware decoder vendors are supporting this method.

I guess the wish list is to add 720p60p for the 1394 output port for any future version of GYHD100s...

[Steve Mullen]

Originally Posted by Steve Kuh

I also checked the MPEG2 Video standard, ISO 13818-2, there is no mention of the Repeat Flag. This may be the reason that not too many hardware decoder vendors are supporting this method.

That's interesting because JVC claims -- and I think I've seen confirmation -- that 1394 connected to 1394 on Sony HDTVs plays back 24P and 30P fine. The JVC 1394 to ASI box also supports 30p.

Either that means RF are in the MPEG2 standard or some/many devices that support ATSC automatically know -- without RF flags -- that 24fps and 30fps must be displayed at 60p or 60i.

And, if RF are not part of MPEG2 -- I wonder how AIC correctly handles 24p? Did Apple decide to support MPEG2 with RF or HDV with RF? And, why doesn't Apple's HDV capture support RF when AIC does?

PS -- stuttering may not indicate no 30P support. Perhaps there is another problem.

[Barry Green]

A Sony XBR960 will play back JVC 24P footage via firewire, I can confirm that. Repeat flags and all.