aaudio: use minimum of one burst in buffer

The old minimum was zero, which minimized latency
but was probably too aggressive for some devices.
It is better to avoid glitches.
Because of other changes in AAudio MMAP, this will
have the same latency as earlier version,
but better immunity from glitches.

Bug: 153589709
Test: launch OboeTester
Test: tap TEST OUTPUT
Test: tap OPEN and START
Test: notice that actual buffer size will be 1 * burstSize
Change-Id: Ie53352a0589c710be11f74e995bd12be4f7c45a8

media/libaaudio/src/client/AudioStreamInternal.cpp

@@ -714,12 +714,8 @@ void AudioStreamInternal::processTimestamp(uint64_t position, int64_t time) {
 aaudio_result_t AudioStreamInternal::setBufferSize(int32_t requestedFrames) {
     int32_t adjustedFrames = requestedFrames;
     const int32_t maximumSize = getBufferCapacity() - mFramesPerBurst;
-    // The buffer size can be set to zero.
-    // This means that the callback may be called when the internal buffer becomes empty.
-    // This will be fine on some devices in ideal circumstances and will result in the
-    // lowest possible latency.
-    // If there are glitches then they should be detected as XRuns and the size can be increased.
-    static const int32_t minimumSize = 0;
+    // Minimum size should be a multiple number of bursts.
+    const int32_t minimumSize = 1 * mFramesPerBurst;
 
     // Clip to minimum size so that rounding up will work better.
     adjustedFrames = std::max(minimumSize, adjustedFrames);
@@ -731,12 +727,14 @@ aaudio_result_t AudioStreamInternal::setBufferSize(int32_t requestedFrames) {
         // Round to the next highest burst size.
         int32_t numBursts = (adjustedFrames + mFramesPerBurst - 1) / mFramesPerBurst;
         adjustedFrames = numBursts * mFramesPerBurst;
+        // Clip just in case maximumSize is not a multiple of mFramesPerBurst.
+        adjustedFrames = std::min(maximumSize, adjustedFrames);
     }
 
     // Clip against the actual size from the endpoint.
     int32_t actualFrames = 0;
     mAudioEndpoint.setBufferSizeInFrames(maximumSize, &actualFrames);
-    // actualFrames should be <= maximumSize
+    // actualFrames should be <= actual maximum size of endpoint
     adjustedFrames = std::min(actualFrames, adjustedFrames);
 
     mBufferSizeInFrames = adjustedFrames;