Lossless and lossy

Lossless is a way of compressing data which is fully reversible -- e.g., does not "throw away" data. A losslessly compressed file can be used to create an exact copy of the source file.

Lossy is the opposite of lossless. A certain amount of data is discarded; how much is usually dependent upon a quality or bitrate setting of the codec. This makes the file (or stream) much smaller that lossless compression, but reduces the quality. It is impossible to transcode from one lossy format to another without further degrading quality.

Lossless Codecs

• WAVE (WAVE is technically a container format, but usually contains lossless PCM audio.)
• FLAC
• WAVPACK
• HuffYUV video codec

Lossy Codecs

• MP3
• Vorbis
• AAC
• AC3
• WMA
• Speex
• Most video codecs