NOTE: This Recommended Practice has been withdrawn. The information contained in it, with updates, has been incorporated into SMPTE ST 125:2013. - This practice describes a means of interconnecting digital video equipment operating in system M (525/60) and complying with the 4:4:4 sampling and encoding parameters defined in ITU-R BT.601, annex 1, with a nominal sampling frequency of 13.5 MHz. Provision is made to carry a fourth, auxiliary, channel as part of the signal multiplex, yielding 4:4:4:4 (or 4×4) overall. - The interface is primarily defined to convey signals having luminance, color-difference, and auxiliary components. Signals having green, red, blue, and auxiliary components may alternatively be conveyed, as described in clause 6. - This is a 10-bit interface, however, provision has been made to interconnect all signals with 8- or 10-bit precision. - The interface consists of two unidirectional interconnections between one device and another. These interconnections carry the data corresponding to the television signal and associated data. - The two interconnections are referred to as link A and link B. Each link shall conform separately to the transmission standards and protocols described in either ANSI/SMPTE 125M or ANSI/SMPTE 259M. - Link A carries all the main channel luminance samples plus those CB and CR samples which are located at even-numbered sample points. - Link B contains the samples of the auxiliary channel (most commonly used for, but not restricted to, key signal information) and the CB and CR samples from the odd-numbered sample points. - NOTE - Although it is common to refer to link A as 4:2:2 and link B as 2:2:4, it must be noted that link A is not a true 4:2:2 signal because the color-difference data it contains were sampled at 13.5 MHz to obtain a 4×4 signal, rather than at 6.75 MHz as specified in ANSI/SMPTE 125M. Therefore, if an attempt is made to use link A as a conventional 4:2:2 signal, there will be aliasing in the subsampled color-difference signals. This quasi-4:2:2 channel could be used for noncritical monitoring, but the full 4×4 signal should be correctly filtered and subsampled before critical use.