Desktop Video: A Starter's Guide to Video Editing

Why, suddenly after years of it being impossible to edit video at reasonable cost on home computers, is the technology suddenly now affordable? Some of the answer has to do with the lowering of computer prices over the past few years, but mostly it results from new, cost-effective video compression.

The only way a home computer can effectively deal with the huge amounts of data required for good quality video is to compress it. To give you an idea of the storage needed for non-compressed video data, here are a few interesting numbers: a 9-second uncompressed (no audio) AVI file takes up 261 Megabytes. That's 29 Megabytes a second. In order to produce a 20-minute video file (with no audio) over 38 gigabytes of storage space would be required. That's fine for George Lucas, but average computer users cannot afford to buy drives like that by the dozen.

To get around this problem, compression formats were devised to dramatically reduce file size, yet retain acceptable quality. These compressors work by throwing out data unimportant to the overall quality of the image.

Take, for example, a blue sky: when you digitize this image there will most likely be thousands of shades of blue present in the image. The compressor takes those thousands of colours and makes them into one, in this case blue. Compressors will also take the movement data out of portions of the video file in which little or no movement are taking place. The consumer often has the choice of how much to compress, while considering final image quality. Our 38 Gigabyte 20 minute file would only take 2.6 Gigabytes compressed in MJPEG format, high quality mode: quite a difference in size, but not a huge difference in quality when viewed on a TV.

Of course, these compression chips and their software were very expensive to produce until recently; but today's CPUs are so fast they can help with a lot of the work, reducing overall cost.

MJPEG: The industry standard, capable of images up to S-VHS quality.
Indeo: Intel's software compression format, most suitable for web based video.
Cinepak: The compression format used most often in QuickTime files.
DV: The format used by Digital Camcorders, very similar to MPEG-2.
MPEG: High compression ratio, tops out at VHS quality.
MPEG-2: Format used by DVD extremely high quality.

The other way to edit video with a computer is to do so with edit decision lists. Using this style the computer only digitizes very small, poor quality clips from the video source. Using these poor quality clips the consumer then uses his or her software to decide what edits are to be made and what transitions are to be produced. After the decisions are made the software and the computer control the camera and automatically do the edits. The only part the computer plays in the editing is producing the transitions and controlling the camera. This method of editing is often quicker than digitizing everything and there is no compression. The only downside is that a very high-end video camera and capture device are required with the proper controls and outputs. One of these control formats is called Control L-Lanc and is only found on very expensive camcorders. Many new DV camcorders can be controlled in a similar way but that is a whole article in itself.

Something that almost all new video editing devices do in some fashion is Smartrender. This allows portions of the video file to avoid being re-rendered when the final output file is created. Previously, all segments of a video had to be re-rendered when the final file was produced even if no changes (besides simple cuts) had been made. Smartrender can figure out if anything was done to a segment and decide to not re-render the file, saving a lot of time in the final rendering process.

All new video-editing devices let you decide about the quality of the final project you are attempting to produce. Depending on your destination medium, you can decide what resolution and compression level is best for your project. If you were developing a video for the web you would use a popular compression format with high compression and a low resolution; if your final output was an S-VHS tape or other high quality format, you would use less compression and a higher resolution. The ability to dictate your quality level is an important tool for desktop video producers.

Skip To Page 1 Introduction • 2 How Does it Work? 3 What Do You Need? 4 Capture Cards and Software 5 Getting Started 6 Professional vs. Consumer 7 Conclusion

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