720p24 Mode Theories

[Steve Mullen]

Originally Posted by David Newman

Wow! It seems that your ideas can't be budged. Sorry, your conclusions are counter to our real world experience of analyzing the transport stream data.

It isn't me that needs to be budged -- you'll have to budge JVC. I have had the HDV tape data structure explained several times to me by JVC. JVC considers it very important that they use the DV track structure and Sony does not. They want the press to understand that point!

I don't see why you have so much believing JVC. Are you really saying they are lying to the press? Or, their engineers don't understand their own technology?

And, if you read the D-VHS spec. doc, they have diagrams of the track structure where the TS bit-stream is packed into groups of 6 tracks.

http://www.jvc-victor.co.jp/english/D-VHS/dvhstr-e.html

David, when you look at the TS bit-stream it is tellling you NOTHING about the tape track structure! The data you see has been already been removed from the tracks. I'm not saying ANYTHING about TS data. I made that clear in what I wrote.

The track structure has an important role in ProHD:

1) It is what will allow PCM audio to be added. JVC engineers explained at great length to me why the PCM audio would be 6-frames ahead of video. That's because all 6 frames of the GOP must be pulled off the tape, before the first video grame can be output. But the very first PCM audio was pulled from the tape on the very first frame! Is JVC Japan feeding me BS?

2) If the structure already has the capacity to hold 720p60 within the 60 tracks -- it means JVC needs to do very little to get 720p60.

3) If the 60 tracks cannot hold the data for 720p60 -- then it will need to be modified for 720p60. If they do this, the JVC way (D-9), they'll speed-up the tape recording 120 tracks/second. (And, that will give us 4-channel PCM audio.)

4) It also allows "trick frames" which is how you can see video during high-speed Forward/Rewind.

5) It holds meta-data.

Bottom-line -- tape always has a structure. Even when it it is recording pure data -- tape always has a structure that holds the data. I don't see, given that JVC is so consistent on this point, why you are having so much problem accepting that the transport streams (what you see) are carried within a structure.

[Guy Barwood]

"I tend to think the 60 tracks can accept 720p60, but is now being used at "half capacity" however that might be be done."

I seriously doubt this Steve. Think of pure data rates. The transport mechanism is at the heart of it a backup drive, with a maximum data transfer rate of 25Mbps. JVC are using the full 19Mbps of 720p for their encoding (or lets face it the artifacts would be pretty rude if it was only using 9.5Mbps for 720p).

So, if JVC want to encode 60p using the same tape transport, they would have to use the same data rate (or up to 25Mbps anyway), and that wouldn't be a good thing.

As you say, they would need to double the transfer rate to tape to allow for 38Mbps which would mean as you suggest running the tape 2x speed or a new tape format with double the density.

Of course, they could also do this like Panasonic are, and only allow the higher frame rates to the likes of the FS4 and limit tape recordings to 30p max.

[Steve Mullen]

Originally Posted by Guy Barwood

"I tend to think the 60 tracks can accept 720p60, but is now being used at "half capacity" however that might be be done."

I seriously doubt this Steve.

Let's see:

1280x720x30 >> 27,648,000 pixels/second compressed into about 18Mbps

1440x540x60 >> 46,656,000 pixels/second compressed into about 23Mbps

1280x720x60 >> 55,296,000 pixels/second compressed into about 18Mbps

What do see here?

1) That 1080i is far more compressed than 720p30 -- which is why 720p30 looks so much better!

2) We can see that: 27,648,000 / 18 >> 1.5:1
verses 46,656,000 / 23 >> 2.0:1

3) How would 720p60 fare? 55,296,000 / 18 >> 3.0:1

4) So while 720p60 would be 2X more compressed than 720p30, it would only be 1.5X more compressed than 1080i is today.

Which why it is possible that JVC will release an HD100 class camcorder with 720p60. And, why I think today's camcorder tape recording structure can handle 720p60.

But I'm totally wrong about "half capacity." Clearly the 720p30 is recorded into the full 18Mbps. It simply looks much better than if 720p60 were compressed to 18Mbps!

Question: would 720p60 look worse than 720p30 at 18Mbps. Perhaps not if the encoder is far better than the one in the HD1/HD10. For this reason I wouldn't rule-out a 720p60 version of the HD100 once the encoder can handle 60fps. For one thing, under motion, it would divide motion into 60 steps rather than only 30 steps -- so the motion vectors would be far more accurate.

Which means there is another approach to 720p60 than writing 120 tracks/second I mentioned in a reply to David. Using a better encoder, 720p60 can be squeezed into the same 60 tracks/second used to today for 720p30.

Which is why I think JVC is talking about a 720p60 "wrapper" on a 30fps camcorder. The wrapper is 60Hz even though today it only carries 24p and 30p -- because it will carry 60p in an HD200.

[Guy Barwood]

"Question: would 720p60 look worse than 720p30 at 18Mbps"

I wouldn't doubt it at all, but that is only my guesswork at play. I know what you mean by the motion vectors being less, however I have to think that your still adding more than your compression gains or 120fps would be better than 60fps again.

[Steve Mullen]

Originally Posted by Guy Barwood

"Question: would 720p60 look worse than 720p30 at 18Mbps"

I wouldn't doubt it at all, but that is only my guesswork at play. I know what you mean by the motion vectors being less, ...

If 19.2Mbps is good enough for broadcast HDTV runing at 720p60 -- why should we think it won't be OK for a next generation HD100. Which is another reason I think the HD100 currrent recording system is ready to carry 720p60. In fact, I doubt it is any different than the HD1/HD10.

I feel like this fact has been staring us in the face all along. JVC chose an ATSC data rate of 19.2Mbps exactly so everything will match an industry standard. Which is why they continue to use record TS while Sony does not.

And, they chose to record this to an industry standard DV tape data structure.

This is pure JVC thinking. It is the way they worked VHS. For decades they kept evolving upon the VHS platform. Enhancement after enhancement. Likewise, with Digital-S (D-9) which is VHS in it's nearly last form. Along with W-VHS and D-VHS.

They'll take 19.2Mbps, MPEG-2 TS, and DV transports as far as they can.

[Guy Barwood]

"If 19.2Mbps is good enough for broadcast HDTV runing at 720p60"
I havn't seen it but I think the question is "is it good enough?".

I have noticed since the intro of digital TV that the quality of what is broadcast is often much less than what I would have thought would be acceptable or termed "broadcast quality". Some content looks simply stunning, but other content looks horrible, full of macroblocks etc. People worry about chromatic abberations in the HD101's lens yet there are far worse villans out there. The quality of the encoder is a huge factor. After all, these things have to be real time encoders, which even our 3.6GHz top of the range CPUs can't achieve while consuming 100+ watts.

If you get your way, I think you'b be left with the choice of either great quality 30p or a unimpressive 60p without throwing more bitrate at it.

Only my opinion though, and you know what they say about opinions, like armpits, everyone has em and most of them stink... (thats the nice analogy anyway)

[Barry Green]

Originally Posted by Guy Barwood

"If 19.2Mbps is good enough for broadcast HDTV runing at 720p60"
I havn't seen it but I think the question is "is it good enough?".

I have noticed since the intro of digital TV that the quality of what is broadcast is often much less than what I would have thought would be acceptable or termed "broadcast quality".

AGREED, with a capital "A" (and capital "G", "R", "E", "E", and a "D"). 19.2 isn't good enough for broadcast. Works okay for "American Idol", but the bitrate is woefully inadequate for sports coverage. Macroblocking and mega-mosquito noise galore.

[Steve Mullen]

Originally Posted by Barry Green

AGREED, with a capital "A" (and capital "G", "R", "E", "E", and a "D"). 19.2 isn't good enough for broadcast. Works okay for "American Idol", but the bitrate is woefully inadequate for sports coverage. Macroblocking and mega-mosquito noise galore.

What you both say is true -- of 1080i60.

But it is definitely not true of 720p60.

I have NEVER seen an MPEG2 artifact on FOX, ABC, or ESPN sports! Never, ever!

But, when there is a burst of fire on an animattion on sports replays -- the fire macro blocks like crazy on 1080i. Perfectly clean on 720p60.

Progressive simply compresses with vastly greater efficiency under motion.

I've also never seen an artifact from my JVC HDV camcorder.

However, I must compliment CBS. They really send out a clean signal! They also refuse to allow cable companies to drop their data rate. It's NBC that gets most of the complaints.

[Steve Mullen]

Hey Barry!

I'm moving to LV in October! Already bought a house and car!

How good/bad is Cox HD?

See you in October!

[Guy Barwood]

There is a way to answer this question. Find out what the HD7000 is going to do.

http://pro.jvc.com/prof/Attributes/f...&feature_id=01

User-selectable Recording Format
HDV: 720/24p/25p/60p/50p, 480/60p, 576/50p
MPEG2: 1080/60i/50i (HDD Only)
DV: 480/60i/24psf, 576/50i/25psf


It won't do 1080p (thats a bit of a shame). We know HDV is 4:2:0, but what about the "MPEG2: 1080/60i/50i". It would be nice to have a 4:2:2 option, especially on a camera your going to spend near on US$30K

[Barry Green]

Originally Posted by Steve Mullen

I have NEVER seen an MPEG2 artifact on FOX, ABC, or ESPN sports! Never, ever!

Then you haven't looked hard enough. There was enough mosquito noise during the NBA finals to make you think you were living in Tennessee.

Granted, it was less than during the NCAA tournament on CBS, but it was still very prevalent and quite annoying.

I've also never seen an artifact from my JVC HDV camcorder.

Then you haven't shot under circumstances where it happens. But that doesn't mean that the JVC is artifact-free, because it most definitely isn't. Get ahold of the JVC demo footage from WEVA, you'll see major quilting and macroblocking in at least one of the shots.

However, I must compliment CBS. They really send out a clean signal! They also refuse to allow cable companies to drop their data rate. It's NBC that gets most of the complaints.

Funnily enough it was the CBS broadcast of the NCAA basketball tournament where I saw the most artifacts. It was downright disturbing. They'd do a slow-mo replay of a shot going through the hoop, then dissolve back to the live action, and I'd swear it looked reminiscent of pixelvision until the dissolve was completed.

Definitely see more problems on 1080i than on 720p though. There I will agree with you, however I disagree that "it doesn't happen" on 720p because it most definitely does. Just not to the same degree as 1080i.

[Barry Green]

Originally Posted by Steve Mullen

Hey Barry!

I'm moving to LV in October! Already bought a house and car!

Wild! Cool! If you already bought a house, it's probably gone up in value by $10,000 so far... real estate's been downright nutty here. Appreciation of 50% just last year alone.

What brings you to LV?

How good/bad is Cox HD?

I don't subscribe specifically to Cox HD... to get that you have to subscribe to digital cable, and all the demos in Best Buy/Circuit City look awful, so I can't be convinced to switch; I'm still slogging along on analog cable. So for most HDTV viewing I'm on OTA. Funnily enough I recently found out that Cox broadcasts the digital signals even over analog cable so you can get them without subscribing to digital cable, but you'll need a set with a digital tuner in it. My XBR scanned the analog cable and came up with all the analog channels, and then it found dozens of digital channels too! Looks pretty good, comparable to OTA. But there are a couple of channels you get with digital cable/HD (like Discovery and InHD) that you don't get on the regular analog Cox Cable... the regular cable sends all the network OTA stations (less WB, for some reason) and a digital version of SD of some of the major stations (like TNT, CNN, WGN, etc).

[Barry Green]

Originally Posted by Guy Barwood

It won't do 1080p (thats a bit of a shame). We know HDV is 4:2:0, but what about the "MPEG2: 1080/60i/50i". It would be nice to have a 4:2:2 option, especially on a camera your going to spend near on US$30K

You may get exactly that. While at WEVA I asked a few pointed questions about this camera to the general manager of product engineering. He told me that it won't be HDV, it will be a new format, and while they're developing a new format, they might go all the way. He said they were not satisfied with the undersampled HDV resolution, and especially that HDV/1080i doesn't support progressive -- he said that they may very well go 1920x1080, including progressive, and that they may go with a higher profile level to get 4:2:2. Since it'll be a brand-new format there aren't any restrictions they have to adhere to. He didn't mention bitrate, but the bitrate question is open as well... may be 50mbps, may be 36mbps, who knows? I believe he said that the MPEG-2 will not record to tape, only to disk -- so it's not limited by the bandwidth of the tape.

[Mathieu Ghekiere]

Again a new HD format, then? Or am I understanding something wrong?

If so, won't it be a little bit too much?
What if every company starts it's own format. Then every NLE has to read it,... will it all be compatible with each other?

[Barry Green]

Originally Posted by Mathieu Ghekiere

Again a new HD format, then? Or am I understanding something wrong?

If so, won't it be a little bit too much?
What if every company starts it's own format. Then every NLE has to read it,... will it all be compatible with each other?

It would be a new format, yes. The GY-HD7000U will record regular ProHD to tape, so in 720p mode it'll be compatible with the others. But in 1080 mode, it would be their own new format, and yes editors would need to be updated to support it.

So the question becomes: is 1920x1080/24p/30p/60i @4:2:2 compelling enough for people to adopt the format? That's the question. The fact they're going disk-based removes a lot of obstacles though -- no need to engineer a new tape drive, no need to make people buy decks, no need for programmers to write capture utilities, etc. It should be a matter of updating their MPEG encoder/decoder to work with the new profile. Who knows, maybe they already do?

Tape is dead (whether it knows it or not). Tape can say "I don't want to go on the cart" all it wants, but the tapeless options are so totally superior. It's tapeless that makes such a new format possible and reasonably practical...