Cinepak is a video codec, developed by Radius Inc, to accommodate 1x (150 kbyte/s) CD-ROM transfer rates.

It was the primary video codec of early versions of QuickTime and Microsoft Video for Windows, later superceded by Sorenson Video, Intel Indeo, and more recently MPEG-4. However, movies compressed with Cinepak are generally still playable today.

Cinepak is based on vector quantization, which is a significantly different algorithm from the DCT (discrete cosine transform) algorithm used by most current codecs (in particular the MPEG family, as well as JPEG). This permitted implementation on relatively slow CPUs, but tended to result in blocky artifacting at low bitrates.