Steps to reproduce:
0. Make sure your Linux machine has ffmpeg package installed, if not, install it.
1. Download the attached project
2. Change build target to WebGL
3. Inspect the editor logs, on reimport process FSBTool outputs this:
Please use -b:a or -b:v, -b is ambiguous
Codec AVOption b (set bitrate (in bits/s)) specified for output file #0 (Temp/importedAudioTempPrimary) has not been used for any stream. The most likely reason is either wrong type (e.g. a video option with no video streams) or that it is a private option of some encoder which was not actually used for any stream.

Reproduced on: 5.6.3f1, 2017.1.1f1, 2017.2.0b11