Encoding 101 Contact Print
   Why Encode?   The Process   Transcoding   Encoding Terms   
 
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Transcoding:

In general, many compressed digital sources can be transcoded to streaming formats, but not all compressed formats transcode well. This is due to the fact that some compressed digital formats also use "lossey" compression methods to achieve higher data transfer rates. When these compressed files are transcoded, areas that have had the original data discarded are recompressed. The result is called an artifact, which is an unnatural spot in the image that is visually distracting. MPEG1, MPEG2, DV and compressed AVIs are all formats that can be transcoded. The process is identical to encoding except the capture phase is not required.

The Encoding Triangle

The Encoding Triangle

As mentioned earlier, the most challenging task in encoding is balancing between a low enough delivery rate to deliver continuously over the target delivery rate and acceptable quality. To achieve this, you must think in terms of a triangle. The target delivery rate is the triangle that is fixed. Priority can then be put on any two corners at the expense of the third. For instance, if your content is fast motion, then image quality and frame rate are going to be important to render acceptable action. With emphasis on these two, the frame size will have to be lowered to keep the amount of overall data required to render the video. If the content is a talking head, with little to no motion, then you can increase the available bandwidth for the frame size and quality by lowering the frame rate. In addition to this main rule, there are two additional considerations:

  • Spacing of "key frames"—The fewer key frames in the video, the less overall bandwidth it will need to stream.
  • You can also adjust the amount of bandwidth allocated to the audio to increase available bandwidth to the video.

In conclusion, encoding is a constant balancing of settings to achieve an acceptable result. With practice and experience, media can be produced to dazzle all Streaming Media users on the Internet.

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