Some manufacturers enable their version of the VIVO port to also transfer sound.
The VIVO output on graphics cards is often not used by those who have no need to connect their computer to a TV. Also, there can be issues in software supporting the use of VIVO ports.
A computer using VIVO must have software that can handle an input signal. For example, in the case of Nvidia GeForce series 6 and 7 video card users this means downloading Nvidia's WDM drivers