diff --git a/media/libaaudio/examples/utils/AAudioSimplePlayer.h b/media/libaaudio/examples/utils/AAudioSimplePlayer.h
index 4557f02..cc0cb34 100644
--- a/media/libaaudio/examples/utils/AAudioSimplePlayer.h
+++ b/media/libaaudio/examples/utils/AAudioSimplePlayer.h
@@ -30,6 +30,11 @@
 #define SHARING_MODE  AAUDIO_SHARING_MODE_SHARED
 #define PERFORMANCE_MODE AAUDIO_PERFORMANCE_MODE_NONE
 
+// Arbitrary period for glitches, once per second at 48000 Hz.
+#define FORCED_UNDERRUN_PERIOD_FRAMES    48000
+// How long to sleep in a callback to cause an intentional glitch. For testing.
+#define FORCED_UNDERRUN_SLEEP_MICROS     (10 * 1000)
+
 /**
  * Simple wrapper for AAudio that opens an output stream either in callback or blocking write mode.
  */
@@ -219,10 +224,13 @@
 typedef struct SineThreadedData_s {
     SineGenerator  sineOsc1;
     SineGenerator  sineOsc2;
+    int64_t        framesTotal = 0;
+    int64_t        nextFrameToGlitch = FORCED_UNDERRUN_PERIOD_FRAMES;
     int32_t        minNumFrames = INT32_MAX;
     int32_t        maxNumFrames = 0;
     int            scheduler;
-    bool           schedulerChecked;
+    bool           schedulerChecked = false;
+    bool           forceUnderruns = false;
 } SineThreadedData_t;
 
 // Callback function that fills the audio output buffer.
@@ -235,11 +243,21 @@
 
     // should not happen but just in case...
     if (userData == nullptr) {
-        fprintf(stderr, "ERROR - SimplePlayerDataCallbackProc needs userData\n");
+        printf("ERROR - SimplePlayerDataCallbackProc needs userData\n");
         return AAUDIO_CALLBACK_RESULT_STOP;
     }
     SineThreadedData_t *sineData = (SineThreadedData_t *) userData;
 
+    sineData->framesTotal += numFrames;
+
+    if (sineData->forceUnderruns) {
+        if (sineData->framesTotal > sineData->nextFrameToGlitch) {
+            usleep(FORCED_UNDERRUN_SLEEP_MICROS);
+            printf("Simulate glitch at %lld\n", (long long) sineData->framesTotal);
+            sineData->nextFrameToGlitch += FORCED_UNDERRUN_PERIOD_FRAMES;
+        }
+    }
+
     if (!sineData->schedulerChecked) {
         sineData->scheduler = sched_getscheduler(gettid());
         sineData->schedulerChecked = true;
diff --git a/media/libaaudio/examples/write_sine/src/write_sine_callback.cpp b/media/libaaudio/examples/write_sine/src/write_sine_callback.cpp
index 01cf7e7..b5602e9 100644
--- a/media/libaaudio/examples/write_sine/src/write_sine_callback.cpp
+++ b/media/libaaudio/examples/write_sine/src/write_sine_callback.cpp
@@ -26,9 +26,7 @@
 #include <aaudio/AAudio.h>
 #include "AAudioExampleUtils.h"
 #include "AAudioSimplePlayer.h"
-
-// Application data that gets passed to the callback.
-#define MAX_FRAME_COUNT_RECORDS    256
+#include "../../utils/AAudioSimplePlayer.h"
 
 int main(int argc, const char **argv)
 {
@@ -42,9 +40,10 @@
     // in a buffer if we hang or crash.
     setvbuf(stdout, nullptr, _IONBF, (size_t) 0);
 
-    printf("%s - Play a sine sweep using an AAudio callback V0.1.1\n", argv[0]);
+    printf("%s - Play a sine sweep using an AAudio callback V0.1.2\n", argv[0]);
 
     myData.schedulerChecked = false;
+    myData.forceUnderruns = false; // set true to test AAudioStream_getXRunCount()
 
     if (argParser.parseArgs(argc, argv)) {
         return EXIT_FAILURE;
@@ -99,7 +98,10 @@
             printf("Stream state is %d %s!\n", state, AAudio_convertStreamStateToText(state));
             break;
         }
-        printf("framesWritten = %d\n", (int) AAudioStream_getFramesWritten(player.getStream()));
+        printf("framesWritten = %d, underruns = %d\n",
+               (int) AAudioStream_getFramesWritten(player.getStream()),
+               (int) AAudioStream_getXRunCount(player.getStream())
+        );
     }
     printf("Woke up now.\n");
 
diff --git a/services/oboeservice/AAudioMixer.cpp b/services/oboeservice/AAudioMixer.cpp
index 8222734..952aa82 100644
--- a/services/oboeservice/AAudioMixer.cpp
+++ b/services/oboeservice/AAudioMixer.cpp
@@ -88,11 +88,11 @@
         }
         partIndex++;
     }
-    fifo->getFifoControllerBase()->advanceReadIndex(mFramesPerBurst - framesLeft);
-    if (framesLeft > 0) {
-        //ALOGW("AAudioMixer::mix() UNDERFLOW by %d / %d frames ----- UNDERFLOW !!!!!!!!!!",
-        //      framesLeft, mFramesPerBurst);
-    }
+    // Always advance by one burst even if we do not have the data.
+    // Otherwise the stream timing will drift whenever there is an underflow.
+    // This actual underflow can then be detected by the client for XRun counting.
+    fifo->getFifoControllerBase()->advanceReadIndex(mFramesPerBurst);
+
 #if AAUDIO_MIXER_ATRACE_ENABLED
     ATRACE_END();
 #endif /* AAUDIO_MIXER_ATRACE_ENABLED */