What’s a constant bitrate?

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Constant bitrate is useful for stable playback of streaming media, but not ideal for archiving complex files. Variable bitrate allows for more flexibility in bitrate modeling.

Constant bitrate is a tool used in digital telecommunication signals, for example when transferring audio files from the Internet. A constant bitrate file is encoded to produce a file that plays at exactly the same bitrate for its entire duration. The biggest benefit of a constant bitrate file type is that it allows for stable playback of streaming media, as the bitrate will never fluctuate, reducing any potential lag and jitter from the server end of the broadcast. While this file type is ideal under such circumstances, it is disadvantageous for archiving more complex file types, as the constant bitrate can be over- or under-utilised depending on variations in the file.

A constant bitrate file is like sand flowing through an hourglass: it will always progress at exactly the same rate. Contrast this with an opposite file type, the variable bitrate file. In a variable bitrate file, the “sand” is clumpy, with the result that sometimes small grains of information seep through and sometimes larger, more complex chunks.

As stated, one of the best uses for a steady stream of bitrates is while playing a media file. Compressing everything within the video or audio file into a single playback strengthens the coherence of the entire file, forcing images and tones to become substantially similar to each other. In a media file encoded in a variable bitrate format, the quality of the file can change dramatically from moment to moment as the bitrate goes up and down like a roller coaster. While a file that uses a constant bitrate will not always have the optimal image quality, as some images may need to be scaled down in appearance to ‘fit’ the selected bitrate, at least the entire presentation will be smooth and fluid for the end user .

It might seem that a file with a constant bitrate is always preferable, but that’s not always the case. Some circumstances tend to favor the ability to model bitrate within a specific range of values. Consider archiving a media archive of popular paintings. While some paintings in the collection are hopelessly complex and require a high bitrate to capture their true essence, others are much simpler and require a much lower bitrate to keep the overall file size down. In cases like this, files using a bitrate that remains constant would generally provide too much or too little storage space for each virtual painting image.

While one solution may be to raise the bitrate “ceiling,” allowing even the most complex paintings to be archived with impunity, this is not optimal from a programming standpoint. Files with higher bitrates require more storage space on your hard drive, as each element in the file is given more room to “breathe” by the higher bitrate. The more space wasted by files whose complexity does not warrant the chosen high bitrate, the more inefficient the solution becomes.




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