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General Video Information Analog When working with video on a computer, analog formats are of interest when they are the source and/or target of the editing process. For example, if you intend to capture from an analog camcorder and record the result of your editing on an analog VCR, it's important to understand the properties and limitations of these media. The main issue with an analog medium is the quality it can achieve, which mostly concerns its resolution - i.e. the amount of detail it can store and display. And, the golden rule with every analog format is every time you copy you lose. This means the copy will always be lower quality than the original, even if the target medium is capable of higher quality than the source. This rule applies even if you capture from one analog source into digital format, and then replay the digital format and record back to analog. Consequently, if you intend to record your work to standard VHS tape, you must start with a source that is higher quality than VHS if you want a reasonable result. Formats The popular analog formats can be grouped into two levels, low-quality and high-quality. VHS and 8mm are low quality, SVHS and Hi8 are high-quality. The VHS-C and SVHS-C variants are identical quality to their standard equivalents, but simply use a smaller cassette with a shorter running time. Digitizing Analog video is converted to digital format using a video capture device. This may be built into the computer's display adaptor, be a card that fits internally into the computer, or be an external device that connects to a parallel or USB port. Some devices also provide an analog output so that digital video can be replayed back to analog format. This is essential if you want to record your edited results to VHS tape, but you won't need it if all you want to do is create VCDs or MPEG files for use on the Internet. Capture format The two principal capture formats are M-JPEG and MPEG. Capture/replay devices almost exclusively use M-JPEG, since this is the optimum format for editing at best quality. They are intended for use where both source and target are analog. Whenever possible capture using a data rate that will preserve the quality of the source, even if the quality of the target is lower. For Hi8 and SVHS sources, this means a data rate of about 3 MB/sec, for 8mm and VHS sources use at least 1 MB/sec.Inexpensive capture-only devices are available that capture in VCD-compatible MPEG-1 format via a parallel or USB port. These are simple to install and good, if the target is VCD or Internet and only limited editing is required. They can also be appropriate even if the source is DV, since all DV camcorders have analog outputs. MPEG-2 capture devices are now available. Some actually do the encoding largely in software and require a powerful processor (usually PIII-500 minimum). They could be used where the target is SVCD (or ultimately DVD), but better results would be achieved by capturing and editing in M-JPEG, then converting to MPEG-2. If the processor is capable of encoding MPEG-2 in real time, then the conversion should not take very long. Connectors Some people are a little confused by analog video connectors. There are two basic analog connectors: composite and S-video. Composite is normally an RCA ("phono") style coaxial connector, while S-video is a small round 4-pin.With composite video, all the information is encoded into a single signal, but with S-video the luminance and chrominance are carried on separate pairs of wires. Using S-video connections should result in less degradation, but is only detectable, if at all, where the material is at least Hi8/SVHS quality.If S-video connections are available, it's generally best to use them. But if not, just use composite. S-video connections are not directly related to the SVHS format. In particular, you don't have to use S-video connections to get the benefit of SVHS's higher resolution. You may loose a small amount of quality by using composite, but you certainly don't reduce SVHS to VHS by doing so. Scart connectors include pins for both composite and s-video signals. An S-video capable device with a Scart connection should use the s-video signal, in preference of composite if it is present. Sources & Targets The table below shows combinations of the most popular source and target formats that are not computer-dependent and the usual methods of getting from any source to any target. Sources are listed down the left, targets across the top. NOTE: There is no entry for converting analog tape to DV. If this really is a requirement, the best solution is simply to use a DV camcorder or VCR with analog inputs and copy the source tapes directly to DV tapes. Then work entirely in DV. |
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Source-to-Target Conversion Table
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These are not the only possible methods of getting from one format to another, but are likely to be the most effective. New products are, of course, being constantly developed, so things can change, but the knowledge of the above will also help you understand how useful a new product you encounter in future is likely be. Conclusion Although there are now many video formats available, the choices when it comes to editing work are not really too complicated. We hope this article has helped clarify the options. |
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