Allow setting default bitrate

[bass-style]

When the player bitrate limit is set to No Limit and Subsonic runs through the Transcoder chain (for example to transcode WAV using the default ffmpeg) it will set %b to 128.

This means when rate limit is set to:
- 32kbps limit = plays at 32kbps
- 128kbps limit = plays at 128kbps
- 320kbps limit = plays at 320kbps
- No limit = plays at 128kbps

What determines this 128kbps value and can it be set as an option?

[Skywatcher]

I believe that's LAME's default value, and the one it will use if you don't specify a bitrate.

[bass-style]

It is lame's default, but this is an issue where the bitrate of 128 is passed to lame/ffmpeg as an argument - overriding lame's default bitrate.
So an issue with Subsonic, nothing to do with lame or ffmpeg.