proxy: Use raw audio instead of opus as audio format
Opus might lead to some clipping on the raw samples and will lower the audio Quality, the asset size is not considered to be an issue and keeping the exact audio format is nicer in general.
Moreover the stream duration differences can lead to ugly bugs and this makes that issue much less probable (and something would be really wrong if it still happens with raw audio).
Closes #2248 (closed) (it doesn't really fixes the issue for the files that are broken, those need manual fixing sadly)