Explore direct OPUS streaming from youtube-dl

[yutotakano]

Many audio sources on YouTube are already in OPUS format. The current code decodes that to PCM regardless of the original format, then reencodes to OPUS.

Pros of current format;

• Allows arbitrary middleware processing, through Conduits (PCM is intuitive math)

Cons of current format:

• Slow since the decode/encode is completely redundant if there's no processing
• Loss of quality since OPUS isn't lossless

Perhaps, in the non-processing variants, we should add another logic to check the original format and stream as-is if it's provided as OPUS. This might complicate the reuse of functions like it is now.

[yutotakano]

This is being done with V2.4.0, however the OPUS format that FFmpeg or youtube-dl gives is within an OGG container, and requires code to parse and unwrap, ala https://github.com/Rapptz/discord.py/blob/1be36c9c3ede72eaa2262dfa0e62cbd8b8929e66/discord/oggparse.py#L50