This patch is based on the git commit detailed below, but with the
configure.ac changes removed.

commit b39563b237f82408bc4929d38d52d6ebd4a513b7
Author: David Beswick <dlbeswick@gmail.com>
Date:   Wed Aug 7 08:03:39 2019 +0200

    fluidsynth: replace deprecated fluid_settings_getstr()
    
    Simply depend on fluidsynth >=1.1.0 which introduced the new function to not
    clutter the code with ifdefs.

diff --git a/src/gst/fluidsynth/fluidsynth.c b/src/gst/fluidsynth/fluidsynth.c
index c3263980..9e407590 100644
--- a/src/gst/fluidsynth/fluidsynth.c
+++ b/src/gst/fluidsynth/fluidsynth.c
@@ -587,9 +587,9 @@ gstbt_fluid_synth_get_property (GObject * object, guint prop_id,
           g_value_set_double (value, d);
         break;
       case G_TYPE_STRING:
-        retval = fluid_settings_getstr (src->settings, name, &s);
+        retval = fluid_settings_dupstr (src->settings, name, &s);
         if (retval)
-          g_value_set_string (value, s);
+          g_value_take_string (value, s);
         break;
       default:
         g_critical ("Unexpected FluidSynth dynamic property type");