Appendix G: 270 Million—A Magic Number in Digital Video
The SDI link carries uncompressed SD video at 270 Mbps line rates. Interestingly, the SDI link can synchronously carry a digitally sampled 625/25 line structure signal (used in the PAL system) or the 525/29.97003 line structure signal (used in NTSC systems) at the same line rate of 270 Mbps. How is this possible, because the two TV systems have apparently unrelated sampling rates? History records that the 525 and 625 analog systems were developed independently of each other. However, the two digital systems have a common sampling rate of 270 Mbps. Let us see why.
In the 625 line system the horizontal line rate is 625 × 50/2 = 15,625 lines per second (LPS, units in hertz). In the 525 line ...
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