Ogg support extend: OPUS codec

[miaulightouch]

Opus provide more effective quality and impressive compression than ogg with major browser support

Especially, opus 1.2 highly improve the music quality with same bitrate. even just 32kb/s, opus still save good quality.

[zardoru]

There's a few observations regarding Opus, as we looked into it for use with raindrop arcade.

• Forced sampling rate: Most BMS/bmson files are using 44,1kHz ogg, Opus seems to enforce 48kHz. The cost for resampling is not little in real time (for resampling if you load the whole audio at once.) Apparently opus 1.2 doesn't suffer from this?
• Size efficiency: In spite of that, we re-encoded a few audio files, using default settings, with no apparent change in size. Some of the files were even larger, presumably because of the sample rate conversion.
• Player support: The bmson spec doesn't dictate supported formats. This is mostly up to the implementation. It might (or not) be trivial to add one extra decoder, but that mostly depends on the tools used to build the players.
  Opus 1.2 seems very recent on the other hand, so it sounds like it's a good idea to look at it again.