Eternal Sunshine of the Spotless Mind Music Video

How does a music artist after composing the music play the musical instruments?
Though they invent aesthetically the music (designing), do they themselves play the instruments or instrument players play the music according to the artist's composition? And suppose if the hired instrument player creates a better version of the artist's original composition does the hired instrument player given the credit as well.

for HQ add &fmt=18 at the end of the url and press enter. A very quick made video ,with my favourite bits thrown in and best song out of the soundtrack by Beck. Soundtrack: BECK – Everybody’s gotta learn sometimes Original: The Korgis – Everybody’s gotta learn sometimes