diff --git a/include/camera/camera2/ICameraDeviceCallbacks.h b/include/camera/camera2/ICameraDeviceCallbacks.h
index 670480b..c57b39f 100644
--- a/include/camera/camera2/ICameraDeviceCallbacks.h
+++ b/include/camera/camera2/ICameraDeviceCallbacks.h
@@ -65,6 +65,9 @@
     // One way
     virtual void            onResultReceived(const CameraMetadata& metadata,
                                              const CaptureResultExtras& resultExtras) = 0;
+
+    // One way
+    virtual void            onPrepared(int streamId) = 0;
 };
 
 // ----------------------------------------------------------------------------
diff --git a/include/camera/camera2/ICameraDeviceUser.h b/include/camera/camera2/ICameraDeviceUser.h
index c850924..619b161 100644
--- a/include/camera/camera2/ICameraDeviceUser.h
+++ b/include/camera/camera2/ICameraDeviceUser.h
@@ -133,6 +133,11 @@
      */
     virtual status_t        flush(/*out*/
                                   int64_t* lastFrameNumber = NULL) = 0;
+
+    /**
+     * Preallocate buffers for a given output stream asynchronously.
+     */
+    virtual status_t        prepare(int streamId) = 0;
 };
 
 // ----------------------------------------------------------------------------