I've been trying to figure out how get the projectm-sdl example to capture music output (not just microphones).  Finally realized that SDL was explicitly dropping the monitor sources.  

SDL/src/audio/pulseaudio/SDL_pulseaudio.c in SourceInfoCallback()

Would it be possible to either make new driver or use an env variable to enable these source?  e.g.

+
+int include_monitor_sinks = -1;
+
 /* This is called when PulseAudio adds a capture ("source") device. */
 static void
 SourceInfoCallback(pa_context *c, const pa_source_info *i, int is_last, void *data)
 {
+    if (include_monitor_sinks == -1) {
+        const char *option = SDL_getenv("SDL_PULSEAUDIO_INCLUDE_MONITORS");    
+        include_monitor_sinks = (NULL != option && 0==strcmp(option,"true"));
+    }
+
     if (i) {
-        /* Skip "monitor" sources. These are just output from other sinks. */
-        if (i->monitor_of_sink == PA_INVALID_INDEX) {
+        if (include_monitor_sinks || i->monitor_of_sink == PA_INVALID_INDEX) {
             SDL_AddAudioDevice(SDL_TRUE, i->description, (void *) ((size_t) i->index+1));
         }
     }