This chapter discusses the codec (coder-decoder or compressor-decompressor), a device or software that performs encoding or decoding of digital signals like video, audio, and speech. The next parts of the chapter highlight various patent pools and video codecs: MPEG- 1, MPEG- 2, MPEG- 4, H.261, H.263, DivX, XviD, MJPEG, WMV, RealVideo. The chapter focuses on the Fourier Transform and the Discrete Cosine Transform along with the other important transforms. Exploration of several digital signal processing, compression, data streaming techniques, and complications involved with codecs concludes the chapter.