commit c6b28f46b8116552ec2b38d1d3c8535df28ba7a1

Author: Anthony Pesch <inolen@gmail.com>
Date:   Fri May 4 20:21:21 2018 -0400

    Added SDL_AUDIO_ALLOW_SAMPLES_CHANGE flag enabling users of SDL_OpenAudioDevice to get
    the sample size of the actual hardware buffer vs having a stream created to handle the
    delta

include/SDL_audio.h

@@ -140,7 +140,8 @@ typedef Uint16 SDL_AudioFormat;
 #define SDL_AUDIO_ALLOW_FREQUENCY_CHANGE    0x00000001
 #define SDL_AUDIO_ALLOW_FORMAT_CHANGE       0x00000002
 #define SDL_AUDIO_ALLOW_CHANNELS_CHANGE     0x00000004
-#define SDL_AUDIO_ALLOW_ANY_CHANGE          (SDL_AUDIO_ALLOW_FREQUENCY_CHANGE|SDL_AUDIO_ALLOW_FORMAT_CHANGE|SDL_AUDIO_ALLOW_CHANNELS_CHANGE)
+#define SDL_AUDIO_ALLOW_SAMPLES_CHANGE      0x00000008
+#define SDL_AUDIO_ALLOW_ANY_CHANGE          (SDL_AUDIO_ALLOW_FREQUENCY_CHANGE|SDL_AUDIO_ALLOW_FORMAT_CHANGE|SDL_AUDIO_ALLOW_CHANNELS_CHANGE|SDL_AUDIO_ALLOW_SAMPLES_CHANGE)
 /* @} */
 
 /* @} *//* Audio flags */

src/audio/SDL_audio.c

@@ -1324,15 +1324,12 @@ open_audio_device(const char *devname, int iscapture,
             build_stream = SDL_TRUE;
         }
     }
-
-    /* !!! FIXME in 2.1: add SDL_AUDIO_ALLOW_SAMPLES_CHANGE flag?
-       As of 2.0.6, we will build a stream to buffer the difference between
-       what the app wants to feed and the device wants to eat, so everyone
-       gets their way. In prior releases, SDL would force the callback to
-       feed at the rate the device requested, adjusted for resampling.
-     */
     if (device->spec.samples != obtained->samples) {
-        build_stream = SDL_TRUE;
+        if (allowed_changes & SDL_AUDIO_ALLOW_SAMPLES_CHANGE) {
+            obtained->samples = device->spec.samples;
+        } else {
+            build_stream = SDL_TRUE;
+        }
     }
 
     SDL_CalculateAudioSpec(obtained);  /* recalc after possible changes. */