There is now a "First Release" version (6/21/2019) of basswebm.dll available at un4seen, packaged with a full CHM documentation file and others, at this address:
http://www.un4seen.com/stuff/basswebm.zip . Can this be an addition for MusicBee 3.4's upcoming betas? Some excerpts from the readme portion:
BASSWEBM 2.4
Copyright (c) 2018-2019 Un4seen Developments Ltd. All rights reserved.
Files that you should have found in the BASSWEBM package
========================================================
Win32 version
-------------
BASSWEBM.TXT This file
BASSWEBM.DLL BASSWEBM module
BASSWEBM.CHM BASSWEBM documentation
X64\
BASSWEBM.DLL 64-bit BASSWEBM module
C\ C/C++ API...
BASSWEBM.H BASSWEBM C/C++ header file
BASSWEBM.LIB BASSWEBM import library
X64\
BASSWEBM.LIB 64-bit BASSWEBM import library
VB\ Visual Basic API...
BASSWEBM.BAS BASSWEBM Visual Basic module
DELPHI\ Delphi API...
BASSWEBM.PAS BASSWEBM Delphi unit
What's the point?
=================
BASSWEBM is an extension to the BASS audio library, enabling the playing of
WebM and Matroska files.
Requirements
============
BASS 2.4 is required (2.4.12 or above is recommended).
Using BASSWEBM
=============
The plugin system (see BASS_PluginLoad) can be used to add WebM support to
the standard BASS stream creation functions. Dedicated WebM stream creation
functions are also provided by BASSWEBM.
The usage information in the BASS.TXT file (from the BASS package) is also
applicable to BASSWEBM and other add-ons.