The drivers for your card needs to support the required extensions, and the hardware needs to support the particular codecs as well. So if you don't have already have encoding/decoding support for the given codec with OGL etc, this won't add it most likely.

The main benefit is that application devs won't need to add multiple hardware decoding/encoding APIs, and can just target Vulkan. Cross platform support in particular is currently a mess due to the different APIs on Windows/Linux/Mac, so this will simplify things greatly. Eventually, driver devs will be able to just support Vulkan too, but that's a long way off.