Why I'm not so thrilled about DV...
I dont know everything about video. (YET!) But I think I know enough to see some areas in which DV developers got it wrong. If one of those guys happens to read this (or anyone else for that matter!), please send me email and tell me what you think. What I say here was not tested by me, or by anyone as far as I know, so if you know better, or think I got it wrong, please tell me.
Well, its true. DV is what we all been waiting for, isn't it? Its broadcast quality in "pocket" size camcorder. Who needs more than that!
I do. We all do!
Some things about this format just makes me want to...
Cassette:
DV stands for Digital Video - the big idea is the digital recording method, not the cassette. The same digital signal could have been recorded on 8mm or VHS cassettes.
The disadvantage of using the old 8mm instead of the new DV cassettes would have been the bigger mechanism required - so there was no "new development" in miniaturizing to boost sales... oh, yeh, and for the manufacturers, a big disadvantage was not being able to rip you off with new "broadcast quality" cassette prices!
BUT they could have made the DV-CAM an 8mm cassette. the DV-CAM has the same dimentions anyway! only its thinner by less then two millimeters. With the 20-25% more space in an available cheep cassette... we could have got better picture quality by using 1:4 compression instead of 1:5, more time or wider tracks for less dropouts!
Like the mini-DV a "Mini DV8" was also possible, without having to use bigger mechanisms!
What were the advantages of using the old 8mm cassette? The most important is Cheep avilable cassettes, and of course backward compatibility: If the new digital circuitry is added to, not replacing the old 8mm analog circuitry, and you could somehow use the head to read the old analog, then you could at least get playback of your old 8mm material. This would have meant that you could have sold your old Video 8 or Hi8 camcorder, buy a new "DV8" and keep all your old cassette library!
What is a guy supposed to do now, with this new DV cassette? keep his old $300 to $1500 worth of old 8mm video equipment just to play back old cassettes? Or maybe buy 100 new DV cassettes (for outrageous price!) and copy all his videos to DV? that would cost more than what you would get for your old equipment! Lets say you decide to leave the 8mm equipment with you, just to play back your cassettes in the years to come. Did you think about maintenance? even if its stored away in a dry place and almost never used, electrolytic capacitors will start to leak after 10-15 years (someone on the net even complained about capacitors on SONY camcorders leaking after 5 years!!!) this means corrosive acid on your camcorder boards - so you can kiss them bye bye in a few years. - oh, I forgot: what about your 8mm library... better spend more money then, to replace all boards. (Only it costs more than a new camera...)
This is a new issue, so you better think about it. Until now we had VHS. 8mm failed to make an entrance to our homes and stayed a "camcorder format" because people were not about to replace their video libraries. So VHS is still here. Its bulky, but its here to stay! 8mm is not as common, so if DV takes over, and its possible it will, for the first time, individuals will have a very serious problem: All those cassettes you made for your kids and your grandsons after them - all will be lost! soon you will have no means of plying them back! The only thing to do is transfer if all to DV. BUT you can not do that!!! remember - there are no analog inputs on DV camcorders!!! Think about it! now do you still want DV to be the system of the future?
Dropouts:
another problem with using small cassettes, is that a lot of information is packed in a very small area. What's so bad about it you ask? well - all magnetic materials suffer a familiar problem: dropouts. A dropout ocurs when small part of the magnetic material is detached from the base film of the tape. It leaves an unrecorded space. in the old analog VHS, it looked like a white line on the screen, and if you had a VCR with good DOC - DropOut Compensation, you probably saw just a momentary local distortion in the picture. dropouts are becoming more serious as you use your cassette again and again. Sometimes a dirty or faulty mechanism could cause a "long" Dropout or even wrinkle the tape. In VHS, the tape was wide and long. A small dropout was undetectable, and a large one was visible but not a disaster. with 8mm, and especially the new 6mm DV tape, the high density means small dropouts seem much bigger, and bigger dropouts make the cassette useless! You not only pay MUCH more for less tape (and less time) you can also use your cassette fewer times before it becomes useless! Its true, that the error correction of DV makes better Dropout compensation, but for a "broadcast quality" format... its not enough. That is way "PRO" DV recorders like the DV-Cam use wider tracks. (and record 45 min on a 60 min tape!)
HDTV
lets face it. PAL and NTSC sucks! We all want to be able to travel with one instrument - not two bulky cameras - one video and one stills! We want video equipment that rivals the quality of the good old 35mm film! All television system cannot provide resolution of more than about 640x480 or 720x512 (PAL) max studio quality. Even the most sofisticaded broadcast equipment will never reach the amazing resolution of 35mm film of about 1200x1500! the only solution for this is HDTV: High Definition TV, witch is unfortunately delayed because of a standard war between manufacturers and... the lack of public interest. Sometime in the future, when manufacturers are done making money over PAL and NTSC, and when new, bigger displays that require hi resolution picture will be available for a reasonable price, then and only then we will see the HDTV come to life.
HDTV will carry about 4 times the information of the current TV systems. Even if DV compression rate would double until then, a bigger cassette will still be required to hold the same recording time. So again In a few years we shell see another format emerging, and the whole story would repeat itself! If only 8mm cassettes where used, a reasonable time could have been recorded on them even in HDTV! The DV format actually defines HDTV recording mode, only I have no idea how when and if we will ever see it.
For conclusion:
The choice of the new cassette for DV shows that the manufacturers spent very little time thinking about the future, and even less time thinking about their clients - us, the consumers. They rather get rich, by throwing us a bone now and then, and expect us to love their products and buy them... not me! and I hope neither will you. Spend some time to tell them what you think! tell them what you want!
Compression:
So its digital. So what? Its true: if you assemble edit all your movies, never adding any titles, never mixing it, adding wipes and so on, than you have perfectly identical copies, with no generation loss.
But, what is not yet realized by many people, is the fact that even when you transfer your DV data to the computer for editing, and keep it all digital: the editing and recording back to DV - you still get generation loss: digital generation loss!
Sounds impossible? Its not! The compression used by the DV format has a lot in common with analog signal: Its compression is not loss-less. Sampling the chroma signal at half sampling rate is just like filtering it in analog systems. Even the DCT process used for compression is very similar to the non linear emphasize / de-emphasize process in analog VCR... the direct copy of digital signal without converting it to analog is similar to directly dubbing the recorded FM signal like done in some pro systems.
The problem with compression is that its not lossl-ess. the information after decompression is not identical to the original. So what? you say, as long as we dont lose more information when copying it again! - here is where you are terribly wrong! A second compression after a decompression process does not yield the same result as the first compression! The input information is different, therefore the output is not the same! the information is weighted before compression. Some areas are compressed more than others according to the amount of information found in them.
Here you should say: If the decompressed information contains less information (some of it was loss during the compression) than the second compression has an easy job! You are right to ask that. If you keep your original image, not changing it in any way, the process will go almost unnoticed. I say almost, because some change in the information is occurring, so every generation is a bit more different. When you add titles or mix the picture with another one, you get totally new information, and the process cuts more.
The problem gets even worse when different kinds of compression are used - like when using mpeg (on DVD, some editing programs, the future digital transmission and so on). Its true, it is a lot better than what we used to have. But far from perfect!!!
From what I read in some broadcasting magazines - people are worried! there is going to be a big chain of codecs (COmpressors - DE-Compressors) in the future - from a codec in the camcorder to the codec in the non linear editing system, and than distributoin copy or compressed satelite link and digital transmission. we might be heading to a worse picture quality than we are used to! or so they say.
what I would like to see in the future DV model: (email me to add your request here!)
there is no reason a DV camcorder will not have:
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