sed and in the case of the old electron tubes, encoded into a composite color signal. In the case of CCDs, the signal is immediately converted from analog to digital format. Sometime in the mid-1970s, composite analog television video began to be converted to digital format and processed for several functional purposes. Two of the earliest uses of digitized video included time base correctors in video tape recorders and synchronization of remote, non-synchronous video through devices simply called frame store synchronizers. Both devices sampled the analog signal, quantized it into representative samples, and stored the samples in memory, to be read out later in time, synchronous with local station video. In the case of the time base corrector, the storage was a few lines, but the frame synchronizer stored a full frame (525 or 625 lines). Over time, digital versions of composite video have become compos- ite digital video and, as one might expect, many incompatible sets of equipment evolved into the marketplace. Relatively mature versions stabilized around sampling rates equal to four times color sub carrier, commonly termed 4fsc and quantized to 8 or 10 bit depth. The indus- try has evolved to a common serial digital interface, defined in SMPTE 259M for 525/60 and 625/50 scanning formats, making up composite and 4:2:2 component signals. SMPTE 259M is a common interface reference for standard definition television (SDTV) studio mixing, switching, special effects, monitoring, and compression 1 BASIC FUNDAMENTALS, DEFINITIONS, AND KEY TERMS equipment. It covers four payload bitrates, 143Mbs (NTSC), 177-Mb (PAL), 270Mbs 525/625 component (4:3 aspect ratio), and 360Mbs component (16:9 aspect ratio). SMPTE 292M is a similar interface covering high definition television (HDTV). The maximum payload bitrate is dependent on the source format of the video signal, but doesn't exceed 1.485Gbs. As in SMPTE 259M, SMPTE 292 is commonly used to refer to input and output signals of various mixing, switching, monitoring, and compre