View Full Version : HDV compression quandry
09-23-2005, 07:17 PM
I really am stumped by this and I haven't read anything about why the HDV consortium decided on using only a 19 megabit stream for compression on 720p. Why didn't they use the full 25mbs like in 1080i? Is there something that I am over-looking, it seems that 6mps could go a long way in compression and it is a waste of very valuable and already limited bandwidth. Is this just sheer stupidity? The whole HDV compression thing makes no sence to me in the first place and the fact that they obviously handicapped an already handicapped format begs the question, what kind of morons collectively decided this? No wonder Panasonic went the P2 route. Is there a clear answer to this nearly wasted 30% info, just discarded before a heavy dose of compression?
Also, why is there so much dissonance towards Panasonic courageous move to see into the future? The HVX200 is a breakthrough revolutionary camcorder. I honestly dream about this camcorder at night time, wishing and waiting to have it here and it seems that more than not people are harping on this camcorder.
09-23-2005, 11:59 PM
When in doubt, why not give the research and development arms of these multimillion-dollar corporations the benefit of the doubt and assume that they actually had good reasons (or at least what seem to them to be "good reasons") rather than just assume that they are exhibiting "stupidity", or that they are "morons"?
Here are the reasons that I can think of:
1) JVC unilaterally decided on 19 mbps. The "HDV consortium" didn't exist when JVC made its consumer high-def format. They made consumer high-def on their own, and introduced it a full six months before there was such a thing as the "high def consortium".
2) The ATSC, the governing body that established what would be the format for high-definition broadcasts in the USA, set the data rate at a maximum of 19 megabits.
3) JVC apparently decided that it would be a good idea to make a camera that was compatible with ATSC broadcasts.
Seems to me that wanting to be compatible with the broadcast standard that would govern the entire country is not "stupid", it's actually rather commendable, isn't it?
On their own, they created the whole MPEG-2-on-a-DV-tape thing, and they set the data rate so that they would be compatible with high-def broadcasts. You could theoretically shoot on a JVC HDV camera and directly broadcast the signal.
You can't do that with the Sony system. The Sony would require being recompressed and downconverted to (you guessed it) 19 megabits before it could be broadcast.
So, was it stupid? Were they "morons"? I don't know that I would call it stupid... I think they had a very distinct reason for doing what they did. Whether it was a valid reason remains to be seen -- I don't think people do a whole lot of broadcasting of direct JVC tapes.
But keep in mind that, on a bits-per-pixel ratio, the JVC's 19 megabit data rate provides for a lot MORE bandwidth, per pixel, than the Sony/Canon 25-megabit data rate! The JVC implementation delivers about .89 bits per pixel, whereas the Sony version delivers about .46 bits per pixel.
Would it have been "better" at 25 megabits? Compression-wise, sure it would -- but then it wouldn't be broadcast-compatible. They made their choice. I think they based it on solid reasoning -- and again, there was nobody out there helping them, they did this totally on their own. Even though the product they came up with (the HD1) was the most horrible high-def camera ever invented, you kinda have to give them props for inventing the whole low-cost high-def market in the first place. And that should probably earn them a little respect, rather than disparaging them as "morons".
If anyone was moronic, it might have to be the ATSC themselves. If they'd settled on 38 megabits, the whole landscape would be much different (and OTA broadcasts of HDTV would be a whole lot better-looking!) The 19-megabit solution is just too low.
09-24-2005, 12:15 AM
"rather than disparaging them as "morons"."
I do give props to JVC for developing an "HD" cam, it was a giant leap and I understand why they used the 19mbps now, but why would Sony Canon and others agree to continue to use the same data rate as an agreed format? Why is it that they use 25mbps for the 1080i and but only 19mbps for 720p, just because 720 still has a better pixel compression ratio than 1080i?. I guess I still don't understand this discrepancy to the full extent. I am really not concerned to much about it because I plan on avoiding HDV as much as possible in the future, if needs require it I will make do. I guess I am the type of person that tries to get every last bit of toothpaste from the tube.
09-24-2005, 12:16 AM
Hey magicchristopher, I don't want it to come across like I'm picking on you... it's just that there are an awful lot of very talented people working to bring out the best products that they can, and at every turn they're armchair-quarterbacked to death. I'm probably just a wee bit out of patience with the attacking thing; maybe at some point we should employ the old idea of having an "attitude of gratitude" that these people have brought down the cost of high-def gear from $70,000 last year to $1600 this year. Sure, it may not be perfect, and no one solution may be what everyone wants, but -- the HDV guys and Panasonic have all made some flat-out amazing advancements, and each has made choices that they believe are the right ones. The market will prove which one was actually "right", but man... a year ago, we would have killed for any of these cameras. The JVC HD100, had it been introduced a year ago, would have OWNED and people would be praising them from the mountaintops...
It was about 7 months ago that Panasonic dropped the ultimate indie announcement: you can have 1080/24p. Nobody had even fathomed that before, nobody'd dared to dream we could get that -- not even the VariCam had that! That was reserved for the $100,000 CineAlta after all. Now Canon's announced that they're delivering a 1080/24F camera in November for under $9,000 and we have a thread here on the forum titled "nobody would buy this camera at $9k". Boggles the mind.
I dunno. I guess all I'm saying is: these companies hire the best and the brightest that they can find. They put out the best solutions they can. And the market will decide. And we should be grateful for the opportunities that we have now, that we didn't have before. Sure we can pester them with wishlists and keep hoping for that ultimate mega-breakthrough, but seriously...
09-24-2005, 12:24 AM
but why would Sony Canon and others agree to continue to use the same data rate as an agreed format? Why is it that they use 25mbps for the 1080i
My personal opinion is that Sony did that because they will never, ever, ever, ever, ever, ever, ever do anything like anyone else does it. They refuse to. It's their corporate motto: "Sony: Like No Other". And the motto before that: "Sony: The One And Only."
JVC introduced high-def at 19 megabits, with 720p. So it was obvious that when Sony entered the market, the only thing we could be guaranteed is that it would NOT be at 19 megabits, and that it would NOT be 720p. They just won't do it. They have to be different.
When the world was going ga-ga for MP3 players, Sony introduced their own portable music player WHICH DIDN'T SUPPORT MP3! Guess how that did in the marketplace. Guess how Sony overall is doing in the marketplace? Two straight years of losses, slashing 10,000 jobs, selling off businesses... the 800lb gorilla's in pretty dire straits.
Well, they've got a new CEO (who's an American -- that's a first!) and hopefully they'll drop this xenophobic attitude and recommit themselves to innovating good product instead of being different for different's sake!
09-24-2005, 04:22 AM
Can I tell you what the genious of the "19" is?
Even if people don't use JVC's cam for aquisition they still might take the 19Mb/s of JVC as the masterfotmat, being able to air it right away... (could be some kind of assurance of the product-line)