Over the years and with the large variety of hardware I've dealt with I've used quite a few of different video inputs and outputs. While I usually have no issue just plugging cables into devices, I really started to wonder how video cables differed from each other.
Could anyone specify the difference between s-video, rgb, rca, component, composite, vga, hdmi, displayport, dvi, and any others I'm forgetting? Why do these cables keep evolving; what does an hdmi cable offer that an s-video cable does not, for example? What are the advantages of using one cable/input over another? Refresh rate? Input lag?
Best Answer
Analogue
S-video, RGB, RCA, component, composite and VGA. You forgot SCART.
The big difference here is between those which run each colour on its own (pair of) cables (i.e. RBG component & VGA), versus those which squash them down to fewer signals.
S-video carries two signals, luminance and chrominance. Composite carries only one. The squashing process introduces noise and fuzziness to the signal, so these aren't suitable for any higher resolution than plain TV.
Another distinction is whether audio is carried. Two of the three RCA plugs are for audio. The other cable types don't carry audio.
SCART can carry either composite or component or both, along with audio.
Analog systems impose no lag beyond the speed of light, which is roughly one foot per nanosecond.
The key metrics for analogue systems are bandwidth and signal-noise ratio (SNR).
Digital
HDMI, DisplayPort, DVI. All somewhat interchangeable, or at least can be converted without "smart" adaptors. Very high noise immunity and easily capable of perfectly reproducing the input signal.
All can carry audio, although audio over DVI is a bit more complicated.
Digital systems tend to buffer frames and impose input lag of one or more frames.
Digital systems are required if you want clear HD video, especially "4k" (which may require particular version numbers of HDMI etc). Analog systems simply do not have the bandwidth. The best you can get is HD-over-component, which involves huge bulky cables of limited length.
The key metric for digital systems is bitrate, often inaccurately called "bandwidth".
Out-of-band control signals
The older analogue systems have no idea what's on the other end of the cable. VGA has a system for identifying monitors called DDC, so computers can pick a suitable resolution. SCART defines quite a sophisticated protocol for communications among TVs, VCRs, satellite units etc.
The three fully digital systems have control side-channels for the same purpose. In HDMI this is called CEC.
HDCP
HDMI signals can be encrypted as a copy-protection measure. A similar system is built into DisplayPort but not widely supported.