Originally Posted by arnyk
You mean HD SDI? HD SDI uses the same general jitter stimulating data format as HDMI. SDI and HD SDI are a serial data interface with video, audio and control information interleaved in a fashion that is reminiscent of HDMI. To some degree HDMI is cheaped down, twisted pair based SDI. But that doesn't mean necessarily higher audio or video quality.
Yes HDSDI = HD SDI and SDI means standard definition 525/625 signals. I don't think the space between the HD and SDI is of any documented standard. In an electrical and low level encoding sense SDI is actually more similar to SPDIF than HDMI.
This is my niche in the industry. And there are some significant differences between (HD)SDI and HDMI. The most blatant issue is that SDI is a single coax. HDMI is in fact a parallel interface because it carries RGB or YpBpR as three LVDS streams and a seperate clock pair to boot. This invites timing skew and is one of the problems with long distance HDMI. Before SDI was invented in the late 1980s, we did use parallel digital video in the 1980s. This was 10 pairs of balanced ECL along a separate clock. 50 feet was the safe maximum for 27mhz clock rate. Not to mention building a routing switcher of any size, you needed 11 levels of switching. I actually installed a very rare 64x64 parallel digital video router in 1989! It almost filled up three 78inch racks! Note too the the earliest HDTV digital parallel interfaces were 20 pairs plus clock at 74mhz all in a DF50 connector! Talk about skew problems over 20 feet! Fortunately this standard died a quick death in favor of HDSDI in the late1990s.
Current standards are:
270mbs for SDTV and compressed HDTV
1.5gbs for HDTV up to 2048x1080@24P 422 (includes 50i and 60i)
2.97 (3gbs) for 1080P, but two 1.5 gig links can carry 1080P 444 as well
6gbs for 4K 24P (very rare) But two 3gbs streams can carry 4K as well as four 1.5gbs streams.
12gbs and 24gbs are in the standards stage.
143mbs composite NTSC
177mbs composite PAL
360mbs 18mhz sampled 525/625 for 16x9
540mbs for early dual link HDSDI 1035i (never implemented to my knowledge)
Not well explained in the Wikipedia reference:
Since SDI has an embedded clock, jitter is even more of an issue than with HDMI. The video is scrambled to remove long strings of ones and zeros. This scrambling has nothing to do with copy protection, although when use for DCI links, the copy encryption algorithms employed are additionally complicated to maintain a DC free stream. Code values 0-3 and 1020-1023 are reserved for sync flags. HDSDI cannot carry full 0-1023 gray scale although nobody worries about the 4 missing values at the extreme ends and in television usage the range is 64-940 for 10 bit and 16-235 for 8bit anyway. We have a set of standard test signals called "pathalogical signals" that are designed to produce long strings of ones and zeros to stress the receiving PLL clock recovery. Serial jitter is well known by digital broadcast engineers
So in theory the audio packets that are encoded very similar to HDMI could have even worse jitter performance than HDMI. But I have never seen any study of this nor would it generate much interest I'm afraid. Embedded audio HDSDI and SDI is very wide spread and the general consensus is that it just works.
And I should note that most broadcast gear is locked to a plant reference signal which with today's technology is often GPS referenced. So the jitter is cleaned up in the receiving device long before it becomes an audio de-embedding issue. Consumer gear generally lacks this level of re-clocking facilities.
One advantage was that it used the same video coax as its analog predecessor so the cost of upgrading an existing video production facility to digial (usually a TV station) was minimized.
Unfortunately this was an unfulfilled promise. The "good" precision analog video cable was Belden 8281/9231. But many stations still used plain old RG59 72-75ohms depending on who made it. Neither of these cables were good enough for SDI, 8281 with a practical max of 100 feet, RG59, less then 50 feet. And most analog video BNC connectors were 50ohm as well as the patch bays. This made no difference at 5mhz analog video but at 270mbs/143mhz, it started to matter. And at 1.5gbs HDSDI forget it. So much of the old analog infrastructure was all replaced for digital video, sometimes again for HDTV. The standard digital video cables these days are all foam dielectric with bonded foil shields for impedance control..