Getting DV on your Desktop
This article was written by Alistair Jackson of EditHouse, and was first published in Desktop magazine in July 2002.
Multimedia has been with us for years now, but until recently the video options for those multiple forms of media have been a pretty woeful collection. For a long time, computers have happily dealt with still pictures (all the dpi and colours you could want - no problem) and audio (mixing and manipulating 64,000 audio levels 48 thousand times a second - a piece of cake), but when is comes to video, (errr, a moving postage stamp sized image refreshed every now and then) until recently most computers preferred to crash.
Over the last couple of years, television quality images have finally been hitting our desktops. Programs like Final Cut Pro and Premiere, not to mention iMovie and the other freebies, have been allowing anyone with a mid-range computer, access to powerful video editing tools.
Top of the range television equipment still costs about $100,000 for a camera, and a similar amount for an all bells and whistles uncompressed video editing system. However, with every new release, the consumer and semi-professional gear gets closer to the broadcast equipment in quality and becomes cheaper at the same time.
Desktop editing solutions have only become possible thanks to advances in the field of digital video compression. The full quality digital video signals that are piped around television stations require 270 Mega bits per second. That requires 34 Mega Bytes of storage per second of video and the ability to read and write to a disk at that speed. However, through the use of video compression, these data rates can be brought down to a more manageable level.
Video compression works in the same way as still image compression. For photos or complicated illustrations, JPEG will take the image and compress it into a fraction of the space required for a TIFF or BMP. The down side is that pixelation and other distortions may become apparent around sharp edges of the image. The DV and MPEG compression systems do the same thing with raw video footage. Any redundant, and some not so redundant, picture information is thrown away. A good compression algorithm will do this in such a way that the human visual system is unable to detect the fact that the picture has been altered.
The DV compression standard is used by the MiniDV, DVCAM and DVCPRO videotape formats. This standard reduces the data rate to 25Mbps, which translates to just over 3 Mega Bytes of storage per second of video. This doesn't sounds so high, but keep in mind that it must be a continuous stream. 100 Meg Ethernet will happily deal with this data rate most of the time, but when packets start colliding and have to be resent, your continuous video stream may come to jerky standstill. Likewise, CD-ROM drives can't keep up with the data rate required by DV. However, despite all this, computer processing power and hard disk speeds are now quite adequate for editing DV material.
So now that you can edit video on your computer, and even burn it to DVD for viewing on your TV, how do you go about acquiring that video material?
A camera is simply a device for changing light energy into electrical energy, and a tape recorder is simply a device for turning electrical signals into magnetic signals and storing them on magnetic tape. A camcorder combines these two functions into the one unit.
The difference in price between one DV camcorder and another has a lot more to do with the camera part, rather than the DV portion. It's the quality and size of the lens and CCD chips more than anything else. All MiniDV camcorders will use the same video encoding algorithm and tape recording format, but if you fail to capture quality pictures to start with, you are stuck with those low quality images forever after. A MiniDV recorder will do a great job of accurately storing those images for you, but there are only limited processing options for improving them.
Once you've shot your footage, it's simply a matter of transferring the encoded information from the magnetic tape of your camcorder to the magnetic disk of your hard drive. The most common way of doing this is with a Firewire (IEEE 1394) cable connecting your camera and computer.
What features determine how good your camcorder is? As previously mentioned, its the resolution of the CCD chips and the quality of the lens which will give you the best pictures. Cheaper cameras have one CCD chip to gather the Red, Green and Blue primaries that make up your colour video image. Better cameras will have three CCD's, with each being optimised for a particular colour frequency.
Other important features are image stabilization and the zoom ratios. An optical zoom is preferable because it will actually increase the size of the image that is scanned by your CCD chip, whereas a digital zoom is going to reduce the resolution of the picture by blowing up the picture after its been captured.
Light sensitivity (Lux Rating) is very important if you plan to do any work in less than perfect lighting conditions. Considering that the camera's sole purpose is to convert light rays into electrical signals, it's clear that there needs to be some light there for your camera to work with. If your CCD chips can't pick up enough light, then your circuitry will have to amplify the signal. By amplifying the signal, the picture looks brighter, which is good, but whenever you amplify a signal, you also amplify any unwanted noise that is present. The result is a picture that has little moving specs, and what was in reality a clear flat portion of the picture of the same colour hue and the same brightness level is now a strange speckly thing.
While a camera is all about light, most people are using their camcorder to record sound waves as well. If this is the case, make sure your camera has good audio specifications and a quality way to monitor the sound as you record it, or at least to check the signal levels.
Programs like Final Cut Pro, edit in native DV format. The stream of bits that go down your Firewire connection and onto your hard drive is unaltered in format from the way it was stored on the tape. That is a major benefit of the system. The minute you compress something, you are actually distorting the picture and reducing its quality. If you then uncompress the picture and recompress it in a different way, you are distorting it further. So, if you use a DV camera, then edit on a DV editing system, and then go back to DV tape, you are doing your footage a tremendous favour. Someone using far more expensive gear, but recording on one format, editing on another, putting it back to a different type of tape, then re-editing again, will end up with more obvious picture degradation than your own humble DV material.
DV is fantastic for many reasons (comparatively cheap, tiny cassettes, editing without conversion in programs like Final Cut Pro), but you don't get all these benefits for nothing. With DV it is more, rather than less, important that you follow good technical production values. Your lighting has to be right, your material should only ever be dubbed or edited digitally, DV to DV, with possibly a final play out to a different format. Just like with still pictures and audio files, keep your footage digital and keep it in the one format. You don't want to convert a TIFF file into a JPEG then back into a TIFF again. Likewise if you've got DV material, then keep it as DV throughout the whole process.
Will a TV station accept my DV masterpiece? If your technical specs are good enough, then there's no reason why they shouldn't. Taking your final product and dubbing it onto DigiBeta or Betacam SP, may be required (and it might be wise not to mention that the whole thing had been mastered on a consumer MiniDV system).