SDI copes with long cable runs better AIUI. It is also more useful if you are in the broadcast arena - as SDI is the standard used to connect broadcast devices (VTRs, Vision Mixers, Routers, Camera CCU outputs etc.) together.
HDMI is a more consumer oriented standard - so in the long run things like IR remote controlled HDMI switch boxes etc. - are likely to be more common (and thus lower cost) than SDI.
Also - SDI is standard def only (HD-SDI is the HD version) - whereas HDMI carries both HD and SD within a single standard.
SDI is one-way only - there is no reverse channel. HDMI is a hand-shaking based format, requiring the display device to be able to talk to the source.
So I take it there are no rules governing the upconversion/scaling of SDI input to component output? So aside from a 'hacked' upconvering DVD player, this is the way to go if you want 1080i over component from a DVD player? Granted, SDI players are modded anyway, but you get my point.
Is SDI output already decoded (MPEG2) - so the quality is still dependant on the specific DVD player you are using (CUE, etc)? Once its decoded however, that signal is sent unmodified out the SDI - correct?
Does anyone know how common if is for DVD players to do extra processing before sending the signal out over HDMI (processing you can't turn off)? The new Pioneer '79ai' is listing HDMI direct mode (pure 480i) as one of its features in there PR material. They specifically mention that there is no extra processing in this mode, unlike the 59ai.
The SDI output is after the MPEG2 decoding. It is effectively the digital 4:2:2 YCrCb uncompressed signal that would otherwise be converted to analogue YPrPb by D/A converters, carried as a serial signal. Often the mods are just simple serialisers and a bit of clock conversion, picking up one or two parallel digital video outputs from the MPEG2 decoder chips and serialising this to SDI.
It uses the same 601/656 sampling scheme (apart from vertical chroma) as MPEG2 used on DVDs and standard def digital TV (which are 4:2:0) The video quality WILL be influenced by the quality of your MPEG2 decoder chipset in your DVD player (or digital TV receiver - there are SDI modded output PVRs and satellite receivers in the UK)
SDI only carries 480i (or 576i) signals, and nothing higher (not 480p, not 576p, not 720p, not 1080i)
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