Don't upload audio to frontend multiple times per frame

[realnc]

It increases the chance of audio dropouts. Also, it's better to submit audio to the fronend after video, as the audio upload can block for a long time and unnecessarily delay video frame presentation.

Fix this by accumulating all audio samples into a single output buffer which is submitted at the end of each frame.

Reviewers

@sonninnos @jdgleaver

[sonninnos]

Thanks! Works nicely here.