HDV 25mbps Im confused

[Bob Horwell]

Hi it's my first posting.
HDV transfers at 25mbps, so what's the benefits over DV? same size CCD's as say DVX100 and same colorspace. More lines on HDV= higher compression? It's 25f (interlaced) what's the benefit of this, uncompress to de-interlace, loose 1080i. I'm really confused about the benefits of HDV. Surely we want 100mbps to make it worth while, to call it Hi-Def. Is it Sony jargon confusing pro-sumers into thinking they can shoot HD?
Hope some of you can clear this up for me.

[Barry Green]

Both DV and HDV use 25mbps encoding. However, HDV uses MPEG-2, which has the potential of being much more efficient than DV encoding. DV encodes every frame as a discrete unit, whereas MPEG-2 in HDV approaches it differently, encoding entire groups of 15 frames in one block, by encoding only one frame discretely, and encoding the following 14 frames as variations/differences from the first frame in the group.

MPEG-2 has its share of problems, certainly -- but when you watch the footage from the FX1, in interlaced high-def mode, on a high-def monitor, it definitely looks like high-def. Not quite like a VariCam or CineAlta, but then again it shouldn't. But it's unquestionably high-def footage, much higher resolution than DV is capable of.

It's not "Sony jargon", since HDV as a format is supported/sponsored by/agreed to by Canon, Sony, JVC, and Sharp.

After spending several days with the FX1, my initial optimism about HDV has turned much more pessimistic -- I think I'd rather (much rather) see a version of DVCPRO-HD implemented in a consumer-level camera, such as Panasonic has teased about.

But to say that HDV isn't HD is to deny the evidence of one's own eyeballs. Look at the footage on a 1080i HD monitor... it's high-definition. It's not raw 1920x1080, but it certainly is an implementation of high-def.

[Bob Horwell]

Thanks Barry. Wow that was quick!! So is the 25f interlaced? if so in your opinion does it look anyhting like the 25p of the XL2? I'm really keen to have a look at the new HDV in feb and i have to agree, if panny can knock out the DVCPRO HD, well happy days :-)

[Laszlo Bodo]

The 25f isn't interlaced. The 50i original footage converted in-camera to 25p isn't interlaced any more.

[Barry Green]

No experience with Cineframe 25. It should be the same thing as Cineframe 30, which is recorded on the tape as interlaced, but looks as if it was captured progressively.

There is no such thing as progressive 1080 footage in HDV. It's all interlaced. However, there's no such thing as Progressive DV, and that didn't stop Canon and Panasonic from implementing it anyway. So in that same vein, Cineframe 25 should look like lower-resolution progressive footage, in the same way as "frame mode" on the Panasonic and Canon cameras looks like actual progressive scan. Each frame is derived from a single point in time, vs. interlaced where they're derived from two different points in time.

In true progressive scan you get the entire frame captured at once, and (at least on NTSC and PAL systems) you can get higher resolution than you can in interlaced.

In 1080 HDV, there is currently no progressive scan, so you have to de-interlace and/or interpolate one field to create the other field from the same moment in time, or perform other types of processes to simulate the look. In-camera Cineframe 30 looks pretty good, it's lower in resolution than raw 1080/60i but still higher-res than DV, of course. I haven't studied the still shots and res charts enough yet to figure out just how much of an impact on resolution it has, and in fact it's very difficult to come to a conclusion on that because what works for a still frame may not work for a moving frame, most especially in an MPEG-2 system like HDV. A still-shot like a resolution chart may show basically full resolution, but a moving shot may drop that to half-resolution, compounded further by MPEG motion compression artifacts... it's tough to answer all the questions, because sometimes you don't even think about ways to test for things until you've already sent the camera back! But I guess that's all part of being out here early on the "bleeding edge" of HDV/1080i.

[Toke Lahti]

<<<-- Originally posted by Barry Green : No experience with Cineframe 25. It should be the same thing as Cineframe 30, which is recorded on the tape as interlaced, but looks as if it was captured progressively. -->>>
Actually all tape formats are recorded in fields.
That's why sony calls progressive formats PsF (progressive segmented frames).

Is it same with xdcam's pd-disks, anyone?

[Barry Green]

24PsF was a modification of a 50i tape mechanism... but I don't believe that all progressive is recorded as interlaced... I'm pretty sure the HDV 720/30p is recorded as pure progressive, and DVCPRO-HD is recorded as pure progressive... unless I'm wrong...

[Dylan Pank]

<<<-- Originally posted by Toke Lahti :Actually all tape formats are recorded in fields.
That's why sony calls progressive formats PsF (progressive segmented frames).

Is it same with xdcam's pd-disks, anyone? -->>>

Actually I thought with digital, it was the other way around - that all video is really progressive, but the CCDs still scan interlaced, and those two fields are printed as one prgressive frame, which was then turned into two fields when it becomes and analogue signal to go to the TV.

Analogue was recorded as fields because the second field followed the first along the linear signal.

Have I been wrong about this all this time?

[Graeme Nattress]

Digital video started as a digital representation of an analogue signal, so digital video can be interlaced because the analogue it was recording is interlaced, or it can be progressive if the analogue signal was progressive.

For progressive to be truely progressive, a whole frame must be made in one instant of time, that instant governed by the frame rate and the shutter.

With interlaced video, for each frame, two instants are recorded, but are stored together combined as a frame which gives many benefits for early television as interlacing is really just analogue compression. For PAL, 50i, you get most of the smoothness and most of the resolution of 50p but in half of the bandwidth, and, that was necessary with early TVs as the electron bean couldn't scan fast enough to make one whole picture in 1/50th second, but it could make a half picture every 1/50th a second.

So no, all video is not really progressive, and digital or analogue really have nothing to do with it.

However, the issue with the FX1 is whether the 25cf mode uses a "good" de-interlacer or not. If it's anything like the CF24 mode, I'd be doing the de-interlacing in sofware where I can properly control it. In FCP, my Film Effects, www.nattress.com did a far better job of making a nice film effect than the CF24 mode by starting with normal 60i footage. If anyone can put up a 50i / CF24 comparison I'd really like to see it!

Graeme

[Robert Silvers]

HDTV broadcasts in the US are 20mbps. HDV is more bits per second than the HD broadcast standard. But sure, you *want* to capture and edit at a higher quality than distribution, so it would be nice if it were 50mbps. In fact, Sony band-limits their studio cameras to 1440x1080 (and the FX1) because they found that 20mbps is not enough for 1920x1080 without overloading the mpeg encoder.

[Bob Horwell]

This has turned out to be very educational, thank you so much for the input guys. I suppose what i'm trying to work out is weather i should sell my DVX100 and go for the new HDV from Sony. I just don't know if it's oranges and apples, as we say in blighty.
Is the HDV really a step forward from the 25p DV on the panny'?

[Robert Silvers]

Well the Sony is not progressive. If you are asking 'does the Sony image clearly look better' then the answer is "Yes, much better."

But if you need 25p to go to 24fps film or some other specific use, then you may want to wait for the second generation which can do some progressive formats.

I am just borrowing the Sony FX1 and won't sell my Canon Optura Xi right now because I could never get any money for it since I broke the flip out screen and also I bought it less than a year ago and don't use video much. But it is a way-better image. Since your camera is more high-end you should sell it before everyone realizes how awesome the new Sony is. There are still MANY people who have not realized that their VX2100s are worthless now.

Yes, the Sony FX1 is the real deal and not an incomplete or poor implementation of 1080i. The camera is incomplete only in that it does not offer 24p, 25p, and 30p and perhaps the next version will or another brand might.

[Barry Green]

Is the HDV really a step forward from the 25p DV on the panny'?

If you're staying in high-def, and exhibiting your work on a high-def display, and you like the "looking through a window" look of interlaced 1080i HD, then yes it's a big step up.

If you're going to be distributing on DVD, no, the FX1 is a step backwards for that.

[Robert Silvers]

But everyone might want to think of the future. While it won't look better on DVD, DVD will be obsolete in 2 years.

If you shoot with the FX1 you can convert it to HD-DVD or Blu-Ray later. Also you can distribute on DVD now with WM9 or other compression.

I shot my wedding in 720P even though I had no way to edit or play it. I still need to get the tapes (Panasonic) onto a hard drive but don't want to spend the money to covert it until it is cheaper. Now if the Sony was out then, I would be editing it already because of the 1394 interface.

[Barry Green]

Some valid points, which is why I acknowledge that if you want to have it in high-def, the Sony is a step forward, a big step forward.

DVD will be obsolete in 2 years.

Whoa. Got to disagree. The consumer electronics industry started pushing HDTV on us 20 years ago, and SDTV has clung on so far, and still accounts for about 97% of the televisions in America, and 99.9999% of the TV's in Europe. It took VHS a long, long time to succumb. I think it's reasonable to expect DVD to be with us for several years, maybe as many as 8 or 10.

Just because a new format may become available, it won't have market saturation overnight! DVD is the fastest-adopted format launch in consumer electronics history, and it took six years for it to penetrate 50% of American households... Six years. And people clung to their VHS players that whole time. And that's just half the households. AND, all those people already owned a TV!

Now compare that to HD-DVD... Something like 97% of American households have no ability to display an HDTV signal. The most optimistic figures I've ever heard are that HDTV is in 10% of American households, a figure I highly doubt. So who will be buying HD-DVD players, what will they be playing them on, and will they really obsolete DVD in just two years? Or five? Or 8?

The most optimistic figure I've seen yet places 50% market penetration of HDTV at the end of 2008. Four years from now. It might take HD-DVD four or five years to become a significant presence in the world's households (other than just among "early adopters"). And every one of those households will still have a regular DVD player.

Standard-def DVD will be a viable distribution format for many years to come.