Transcoding converts media from one encoded form to another. It can change the codec, resolution, bitrate or other properties when the processing workflow supports those changes. It uses computing resources and can introduce quality loss or delay. A player setting cannot assume that a server will transcode a source merely because a device needs another format.
A practical example
A media server might convert an unsupported video encoding into one suitable for a particular receiver. If no conversion service is provided, the receiver instead needs its own compatible decoder or a different available source for that programme.
A common misunderstanding
Increasing a transcoded file's resolution does not restore detail absent from the original. Also distinguish an actual encoding conversion from simply changing the container around unchanged media tracks.
Related terms
Further reading
Stable technical definition. Editorial approach