GitLab

Summary:
Pull Request resolved: https://github.com/pytorch/audio/pull/3104

Continuation of StreamWriter refactoring

This commit extract Encoder (+muxer) from OutputStream

Reviewed By: nateanl

Differential Revision: D43610887

fbshipit-source-id: 30a9862b1aabd5af331ce3f33a5815df1decbad1