Transcoding

Transcoding means converting a file from one encoding method (i.e. file format) to another. Transcoding can be performed from lossless to lossless, from lossless to lossy, and from lossy to lossy.

Special note on lossy transcoding

Every time you encode with a lossy encoder, the quality will decrease. There's no way to gain quality back even if you transcode your 128kbps MP3 into a 320kbps MP3 (or any other high-quality compression).

Transcoding to a lossy format is therefore not recommended, unless absolutely necessary e.g. for portable player use. It will always end up to a worse quality file than the source.