This is a ported and significantly modified version of TinySoundFont by
Bernhard Schelling.   https://github.com/schellingb/TinySoundFont

TinySoundFont lets you use a SoundFont2 library (sampled MIDI instruments)
to play high quality music with a single #include.

Porting and modifications done by Earle F. Philhower, III 
<earlephilhower@yahoo.com> and released under the GPL v3 or later.

The changes to allow it to work on the ESP8266 consisted mostly in making
it significantly less memory intensive and speeding up the inner loops by
 using fixed point arithmetic instead of floating point.  This change to
fixed point lets us use simple integer math, which is massively faster than
the software FP libraries on the ESP8266, but does come at the cost of a
slightly increased noise floor.

On the memory side, all data structures were converted into a "lazy"
allocation which means that instead of loading the full contents of the
header bits into RAM (which is often WAY more than the 40KB available on
the EPS8266), only those bits needed are loaded, and only when they are
needed.

Also, instead of loading the entire sample array into memory (i.e. nearly
500MB for a good piano sample), only a very small portion is loaded into a
LRU *cache* area.

Even with the caching, it was found that SPIFFS, while having great
functionality, was horrbly slow.  So I wrote a new "faster" ROM filesystem
called, surprisingly, FastROMFilesystem.
https://github.com/earlephilhower/ESP8266FastROMFS
If you are getting choppy playback, try this new filesytem or using a SD
card (not tested by myself, but it'd be hard top be slower than SPIFFS).
Simply going from SPIFFS to FastROMFilesystem took my testing of
FURELISE.MID and 1MGM.SF2 from 0.5x realtime to 2.5x (i.e. from unusable
stuttering to plenty of time to do other tings on the ESP8266) for the
first 20 seconds or so tested.

-Earle F. Philhower, III
 earlephilhower@yahoo.com