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- How Video Compression Works
- Source Quality
- Frame Motion
- Encoding Tips
- More Information
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Source Quality
The quality of your source video is determined as soon as you press the recording button on your camera. What follows are some basic guidelines for recording source video that will help you get best possible compression results later on.
- Use a tripod to reduce camera movement. If your camera is not steady, most of the image will move, causing a high percentage of pixels in the video to change from frame to frame and resulting in poor compression quality. A steady camera reduces the number of pixels that change from frame to frame, giving you better quality at higher compression rates (lower data rates).
- Use good lighting techniques. Well-lit subjects are critical for acquiring high quality video. A high-end camera resting on a tripod can still produce a low-quality image if there is not enough light. Low-light or light-gain filters produce video noise on the image. This type of noise is different for each frame of video and makes it difficult for the codec to compress. You might need to use or exceed your maximum data rate to compensate for all this introduced video noise, so use proper lighting techniques on your subjects whenever possible.
- Use the best camera possible. Low-grade cameras—specifically consumer-based ones that record an analog signal on magnetic tape (VHS, Hi-8, and so on)—produce a lot of video analog noise. Still digital cameras in movie mode also have limited quality and generally produce high-noise video clips. Even if the camera is on a tripod with excellent light, these cameras produce noise that causes a lot of problems later when encoding.
- Do the best you can with what you have. High-end digital cameras, digital Betacam camcorders, and 35mm film cameras produce a clean image if the scene is well-lit and they are stabilized by a tripod. Such a scenario produces the best compression ratio and enables you to reduce the data rate while maintaining excellent quality. However, you might not have access to professional equipment, a tripod, or excellent lighting conditions. Just remember: the higher the quality of your video source and the less noise in that source, the lower the data rate required to render a good playback file.
- Whenever possible, always encode a file from its uncompressed source. When converting precompressed digital video into the FLV format, the first compressor has already performed its encoding and reduced the quality, frame size, or frame rate of the clip. Compressing again does not accomplish anything other than introducing digital artifacts or noise. This additional noise affects the FLV encoding process and might require a higher data rate to play back a good-quality file.