SDI (Serial Digital Interface) is/was a standard using old-style BNC (Bayonet Connectors) on heavy well-shielded cables to send COMPONENT RGB or YCbCr video signals out to professional recording decks usually being super-high data rate digital tape or big hard drive arrays! The signal was able to be kept as clean/little-noise as possible and SDI is mostly used in Sports Stadiums, Concert Venues or in Closed Circuit Television systems for commercial/industrial sites connecting high-end SDTV, HDTV or 4K/8K cameras to a central location for recording and long-term storage.
They have updated the standard to include fibre optic BUT SDI is now being overshadowed by 100 Gigabit and 400 Gigabit Ethernet over Fibre which uses a VERY THIN and flexible long-run (up to 5km) single-mode glass fibre OR multi-mode short-run plastic fibre up to 500 metres!
XLR (aka Cannon Connector -- i.e. with TWO 'n's!) sends electrically GROUNDED 3-pin analog AUDIO signals to your off-board recording device OR is used for connecting higher-end microphones (i.e. Neumann U87ai) to your camera or to an external recording device. XLR does not have a video signal on it. Only audio, SMPTE timecode or MIDI-pulses (MIDI = Musical Instrument Digital Interface) for music device and lighting control purposes are sent over this type of connector.
Nowadays, you really should be looking at a camera that has a 10 Gigabit, 100 Gigabit, 400 Gigabit (or even One Terabit!) over Ethernet fibre optic interface which can send multiple channels of Audio Samples, Video Frames, SMPTE Timecode, MIDI pulses and other Metadata interleaved within each Ethernet Frame and upper-level IPv6 TCP or UDP packet.
P.S. Just for a fun fact, BNC cable is heavy as heck! I used to have to pull THOUSANDS of metres of it through all sorts of tight, smelly, bug-infested utility ways for all those sports cameras used in a typical pro-level Hockey game (NHL) or Football (CFL) Game and THEN I had to carry 60 lbs worth of Betacam SP/HDCAM camera, NICAD batteries and wireless audio/video packs on my shoulder for two to four hours at a time! Fibre Optic Cable is soooooooo much lighter and easier to pull than SDI/BNC cable! No wonder our producer/director had a portable hot tub put into the rest tent! Your entire body ACHES after all that sort of physical exertion!
Now You Know!
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