From d9f12e44dc789384b3f8987c9b9033f96057ab32 Mon Sep 17 00:00:00 2001
From: Ken Cooke <ken@highfidelity.io>
Date: Fri, 12 Aug 2016 11:31:06 -0700
Subject: [PATCH] Add resampler support for downsampling with variable-input
 constant-output buffering mode

---
 libraries/audio/src/AudioSRC.cpp | 18 ++++++++++++++++++
 libraries/audio/src/AudioSRC.h   |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/libraries/audio/src/AudioSRC.cpp b/libraries/audio/src/AudioSRC.cpp
index 5dba63b349..44326e5bc4 100644
--- a/libraries/audio/src/AudioSRC.cpp
+++ b/libraries/audio/src/AudioSRC.cpp
@@ -1030,3 +1030,21 @@ int AudioSRC::getMaxInput(int outputFrames) {
         return (int)(((int64_t)outputFrames * _step) >> 32);
     }
 }
+
+// the input frames that will produce exactly outputFrames
+int AudioSRC::getExactInput(int outputFrames) {
+    //
+    // For upsampling, a correct implementation is more complicated
+    // because it requires early exit of the multirate filter.
+    // This is not currently supported.
+    //
+    if (_upFactor > _downFactor) {
+        return -1;
+    }
+    if (_step == 0) {
+        int64_t offset = ((int64_t)_phase * _downFactor) % _upFactor;
+        return (int)(((int64_t)outputFrames * _downFactor + offset) / _upFactor);
+    } else {
+        return (int)(((int64_t)outputFrames * _step + _offset) >> 32);
+    }
+}
diff --git a/libraries/audio/src/AudioSRC.h b/libraries/audio/src/AudioSRC.h
index f7becc22c3..5ae5318b5e 100644
--- a/libraries/audio/src/AudioSRC.h
+++ b/libraries/audio/src/AudioSRC.h
@@ -48,6 +48,8 @@ public:
     int getMinInput(int outputFrames);
     int getMaxInput(int outputFrames);
 
+    int getExactInput(int outputFrames);
+
 private:
     float* _polyphaseFilter;
     int* _stepTable;