How to transform a serial RGB analog signal to parallel analog signals?
The RGB analog signal spec is ENOB=8bit, 10MEG at least.
The purpose of the question I ask is I want to save three DACs into one DAC.
Generally, the current steering video DAC can operate in high frequency like 100MEG.
So, is there a circuit to do this transformation?
Like use "one high frequency DAC+Sample and hold" to replace "three DACs"?

RGB is coded in time domain. It's NOT a compression signal like NTSC.
The TV encoder first generates the digital codes and these digital codes are transformed to analog signals by a DAC.
There are R G B three signals, so we need three channels to do this.
Every one channel has one DAC, so there are three DACs.

What is the loading on the output?

The reason that most video systems use three DAC's is because the output ends up driving 75 ohm coax, and three current steering DAC's get it done fairly well.

If it is a high impedance load (internal to chip lets say, then sample/holds and some phase shifting gets it done.