diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index 6eeda9a..1c277ce 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -1623,8 +1623,8 @@
     bool isTimed = (flags & IAudioFlinger::TRACK_TIMED) != 0;
 
     // client expresses a preference for FAST, but we get the final say
-    if ((flags & IAudioFlinger::TRACK_FAST) &&
-          !(
+    if (flags & IAudioFlinger::TRACK_FAST) {
+      if (
             // not timed
             (!isTimed) &&
             // either of these use cases:
@@ -1633,11 +1633,11 @@
               (
                 (sharedBuffer != 0)
               ) ||
-              // use case 2: callback handler and frame count at least as large as HAL
+              // use case 2: callback handler and frame count is default or at least as large as HAL
               (
                 (tid != -1) &&
-                // FIXME supported frame counts should not be hard-coded
-                frameCount >= (int) mFrameCount // FIXME int cast is due to wrong parameter type
+                ((frameCount == 0) ||
+                (frameCount >= (int) mFrameCount)) // FIXME int cast is due to wrong parameter type
               )
             ) &&
             // PCM data
@@ -1655,17 +1655,35 @@
             (mFastTrackAvailMask != 0)
             // FIXME test that MixerThread for this fast track has a capable output HAL
             // FIXME add a permission test also?
-          ) ) {
-        ALOGW("AUDIO_POLICY_FLAG_FAST denied: isTimed=%d sharedBuffer=%p frameCount=%d "
+        ) {
+        ALOGI("AUDIO_OUTPUT_FLAG_FAST accepted: frameCount=%d mFrameCount=%d",
+                frameCount, mFrameCount);
+        // if frameCount not specified, then it defaults to fast mixer (HAL) frame count
+        if (frameCount == 0) {
+            frameCount = mFrameCount;
+        }
+      } else {
+        ALOGW("AUDIO_OUTPUT_FLAG_FAST denied: isTimed=%d sharedBuffer=%p frameCount=%d "
                 "mFrameCount=%d format=%d isLinear=%d channelMask=%d sampleRate=%d mSampleRate=%d "
                 "hasFastMixer=%d tid=%d fastTrackAvailMask=%#x",
                 isTimed, sharedBuffer.get(), frameCount, mFrameCount, format,
                 audio_is_linear_pcm(format),
                 channelMask, sampleRate, mSampleRate, hasFastMixer(), tid, mFastTrackAvailMask);
         flags &= ~IAudioFlinger::TRACK_FAST;
-        if (0 < frameCount && frameCount < (int) mNormalFrameCount) {
-            frameCount = mNormalFrameCount;
+        // For compatibility with AudioTrack calculation, buffer depth is forced
+        // to be at least 2 x the normal mixer frame count and cover audio hardware latency.
+        // This is probably too conservative, but legacy application code may depend on it.
+        // If you change this calculation, also review the start threshold which is related.
+        uint32_t latencyMs = mOutput->stream->get_latency(mOutput->stream);
+        uint32_t minBufCount = latencyMs / ((1000 * mNormalFrameCount) / mSampleRate);
+        if (minBufCount < 2) {
+            minBufCount = 2;
         }
+        int minFrameCount = mNormalFrameCount * minBufCount;
+        if (frameCount < minFrameCount) {
+            frameCount = minFrameCount;
+        }
+      }
     }
 
     if (mType == DIRECT) {