Jvc Gy-hd250

[Barry Green]

Originally Posted by Steve Mullen

The HD100 is already ProHD so it is "free" of the HDV format.

?

The HD100 carries an HDV badge on it.

According to JVC, ProHD is a catchall marketing name that could encompass multiple formats. But ProHD is not a format. HDV is the one and only format of the HD100.

[Steve Mullen]

Originally Posted by Barry Green

But ProHD is not a format. HDV is the one and only format of the HD100.

Where does your comment come from? I never said ProHD was a format.

I said JVC was "free" of the HDV format specs -- meaning they were "free" to inovate. Now when they do so, they have the option to do what Canon did, and petition for a change of the HDV spec. But, they have two other options: remove the HDV badge and use a ProHD badge, just like Sony has XDCAM HD. Or, the HDV organization may allow them to keep an HDV badge as long as the camcorder meets ALL minimum HD1 specs.

My point was that JVC clearly has the freedom to add features -- and it really doesn't make any difference to THIS thread how JVC badges the new camcorder. So back on topic -- JVC has described some things they would like to do. PCM audio is one. 60p is another.

From what's been published, we already know we'll be getting 60p in an HD100 packaged camcorder -- GY-250.

My tests show PCM is already available on the HD100 -- but it's distorted. So my ONLY question is, will we get clean PCM audio?

[Thomas Smet]

Originally Posted by Stephen L. Noe

Right Nate, however, the math for 15GOP is much more efficient than 6GOP. I would think at 6GOP and double the fps then the datarate would double (minus the audio which would remain the same). This is, of course, keeping the same compression scheme as the current encoder in place.

We'll see....

I hope I get this right. I hope Steve Mullen can help me out with this one.

Anyways using the great article Steve wrote about the efficency of GOP based encoding I do not think a 15 GOP is all much more efficient than a 6 GOP.

If the datarate was increased to the full 25 mbit and switched to a 15 frame GOP I think we would only see about a 50% increase in efficency at the cost of more problems with B and P frames. We would not see a 2x increase to cover the 2x data increase.

I used Steve's model of:
18.7 mb/s 6GOP at 30p = 1.496 per I frame
25 mb/s 15GOP at 30p = 2.2727 per I frame
25 mb/s 15GOP at 60p = 1.13636 per I frame

I hope all of this is right.

If this is right then I cannot see any way to get the exact same quality as 30p unless they went to a 126 GOP at 25 mb/s which I cannot see.

1.13636 per I frame might not be all that bad however. Progressive mpeg is very eficient and the frame changes in 60p are very small compared to 30p.

[Thomas Smet]

Here is another thought. In DVCAM recordings doesn't the tape run at a speed of 150% compared to DV? For example only recording 40 minutes on a 60 minute tape. Couldn't this be modified to put a DVCAM transport in the 250 to give a max of 37.5 mb/s on a dv tape at the expense of a 40 minute record time?

I know DVCAM is still at 25 mb/s but the tape does go faster to fit this over more area of the tape to make it holdup better.

[Steve Mullen]

Unfortunately, I can't comment for a week AND even if I could, I am missing one crtitical item of information. Bottom-line, I'm wondering exactly the same things you guys are running.

Since JVC invented the dual-head design for writing a 2X higher data rate to tape -- and Panasonic uses this for DVCPRO50, JVC certainly COULD write 35-40Mbps to tape.

But, this makes more sense for full-sized DV tape camcorder. Although, 30mins per tape is not a killer to me to be able tohave 60p.

[Tim Le]

Originally Posted by Steve Mullen

Although, 30mins per tape is not a killer to me to be able tohave 60p.

I definitely don't mind giving up some run time for 60p or maybe lower compression at a higher data rate at 24/30p. For me 60p would be used in specialized situations anyway, so it would be nice to have that option with the only compromise being run time.

[Steve Mullen]

Originally Posted by Tim N Le

I definitely don't mind giving up some run time for 60p.

We already know dual-heads can work with DV tape. Anyone used to film or Beta SP would not find 30 minutes a horrible record time.

[Ken Hodson]

JVC uses a 12GOP on all their HDV cams 480p60 modes. To keep the GOP at 12 in the 720p mode they would need to increase the data rate past 19Mb/s.

[Steve Mullen]

Originally Posted by Ken Hodson

JVC uses a 12GOP on all their HDV cams 480p60 modes. To keep the GOP at 12 in the 720p mode they would need to increase the data rate past 19Mb/s.

They do not NEED to do so.

Remember, 720p30 NEED only be encoded at about 8Mbps to be equal to ATSC's bit reduction ratio for 720p60 (16Mbps). The fact that JVC used 18.5Mbps was an OPTION -- much like some broadcasters who use 18.5Mbps for 720p60.

Sony likewise took the OPTION of using 25Mbps even though ATSC 1080i60 uses only 18.5Mbps.

Therefore, there are only two issues for JVC:

1) How much does the drop from 15-frames per GOP to 12-frames per GOP increase the bit-reduction ratio verses how much does the shorter (12-frame) GOP increase motion handling ability verses the ATSC 15-frame GOP? I suspect from an "overall quality" view it is a wash.

2) Will JVC make use of super efficient compression engine that matches the power of those used for ATSC broadcasts? Remember, any data-rate's relation to quality is dependent on the codec. Since there are few -- if any -- motion artifacts on 720p60 broadcasts, there is no reason to believe progressive 4:2:0 video with a frame size of 1280x720 needs more than 18.5Mbps.

[Ken Hodson]

I'm sure they could, but wouldn't that be one heck of a high performing and expensive compression system. Heat, cost, power consumption, I guess would all be factors.

[Matt Davis]

Originally Posted by Steve Mullen

We already know dual-heads can work with DV tape.

I vote for a camcorder that does SDI and HD-SDI really well. FireWire is a bit for bit copy, but hands up anyone who's taken PD150 footage through S-Video to a better codec to improve over DV?

Just thinking out loud here...

I'm sad that the JVC HD100 was kyboshed for me because it didn't play nice with FCP in PAL HDV. Having since worked extensively with Z1s shooting HDV and delivering DV, I'm a believer in HDV as an SD acquisition format. But it could be better...

So...

Is there a situation where JVC (and perhaps Canon) could just dance away from the whole FCP/NLE compatibility thing and concentrate on an absolute killer txfer from whatever format it chooses to record... only to output it as SDI and HD-SDI? Okay, so I may need to pack something like an AJA converter to work with a laptop, but I'd hope to get timecode and the rest.

That way, any camera could choose any compression system to capture, then all cameras and all NLEs decide to txfer the data via the SDI/HD-SDI interface, and the NLE can decide which codec IT will use - Uncompresed, DNxHD, AIC, DVCPro-HD, etc. Suddenly its like film stock - it's not like if you like Fuji you can't edit on a Steenbeck because they only do Kodak. Who cares? (apart from the DoPs) - it's like printing a neg to a workprint and to then neg cut to whatever. Oops... Showing age...

It's just that I've been working with a Z1 in HDV mode with my own Picture Profile, and, well, "stuff HD - it's a great SD workflow". I can do DV for quickies, DVCPro-HD for 4:2:2 stuff, and I can still do Offline PhotoJPEG for high shooting ratios. Who cares what shooting format (aka "neg stock") is used. Do the pix look good? Fine. Use them. We can combine HDCAM, HDV and whatever JVC cook up that enables great footage. Even some Canon HDV stuff too.

Shoot on a format that works for you, ingest through a gateway that works for everyone, then I can work in a format that works for me (with my editor hat on).

:-) Donning the asbestos underpants...

[Wayne Morellini]

Well, I hope that they go to 50Mb/s, or at least 35Mb/s, they have to for their 1080p 7000 model, and 60fps. I hope that it is the same price as the 100, or cheaper, and the 100 will go to half the price. I hope even 4:2:2, but one thing I definitely hope for, that they replace those ... sensors with Altasens 720p 1/2 inch models. I also hope they replace the 100, with something with better sensors, and higher data rate, but I doubt this year.

[Ken Hodson]

Wayne, share the drugs man.

[Wayne Morellini]

Yeah.., I know what you mean, I keep seeing this HD camera the price of a small car in China, and a $3K camera that looks like a HD version of the GR-DV3000, with lower light range and low light capability. How is that possible, must be smoke drifting around here. And then there is this other camera, I keep seeing this cheaper camera marked "HC1" instead of HD1, for $1.5K that can't be right, what does HC1 mean, Hi Capacity? And in a dream they sold tens of thousands of them really quickly and took the market from the first giant, whoops, got to avoid tripping over things ;)