codec/pcm Refactor the code as an io.Writer

Refactoring the pcm.Apply() function as a io.Writer could be beneficial for external developer work. Having the code formatted this way would allow for external developers to be familiar with the interface without having to have a deep niche understanding of the code application.

This change could potentially also allow for easier integration in other pre-existing functions as the interface is more commonly implemented and used across go packages.