A shell variable is a variable that is available only to the current shell. In contrast, an environment variable is available system wide and can be used by other applications on the system.A shell is the operating system's command interpreter. It processes the commands entered on the command line or read from a shell script file.
Transcoding is the process of converting a file from one encoding format to another. This allows the conversion of incompatible data to a better-supported, more modern form of data. Transcoding is often performed if the target device does not support the format or has only limited storage capability.
Transcoding is widely used in mobile phone content adaptation as well as in multimedia message servicing. Transcoding technology is also implemented in home theater PC software, enabling disk space reduction.
Transcoding is often used to covert video formats. It allows graphics and HTML files to be used in mobile devices and other Web-enabled products with small screens, lower bandwidth and comparatively less memory. Transcoding is implemented using a proxy server, which receives a file and uses any particular format to change it according to the client.
The transcoding process changes the bit stream format of one file to another file without any other encoding and decoding processes. This is generally effective only if the source and destination formats are alike. The data file is decoded to an uncompressed format and further encoded into a target format.
There are three types of transcoding:
Transcoding with a lossy encoder decreases quality. The drawback of this process is that the resultant quality is never regained. However, this method is still used to lower bit rate in portable players, where the listener is less concerned about sound quality than saving storage space.
Lossless to lossless transcoding is recommended to avoid quality disruption. Transcoding from a lossless source to a lossy target requires keeping the lossless source files. This allows for re-encoding if the lossy result is not adequate.
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