diff --git a/core/jni/Android.bp b/core/jni/Android.bp
index 302189f..d4903d8 100644
--- a/core/jni/Android.bp
+++ b/core/jni/Android.bp
@@ -165,6 +165,7 @@
         "android_media_JetPlayer.cpp",
         "android_media_MediaMetricsJNI.cpp",
         "android_media_MicrophoneInfo.cpp",
+        "android_media_midi.cpp",
         "android_media_RemoteDisplay.cpp",
         "android_media_ToneGenerator.cpp",
         "android_hardware_Camera.cpp",
diff --git a/core/jni/AndroidRuntime.cpp b/core/jni/AndroidRuntime.cpp
index 01ca054..11f3558 100644
--- a/core/jni/AndroidRuntime.cpp
+++ b/core/jni/AndroidRuntime.cpp
@@ -108,6 +108,7 @@
 extern int register_android_media_MicrophoneInfo(JNIEnv *env);
 extern int register_android_media_JetPlayer(JNIEnv *env);
 extern int register_android_media_ToneGenerator(JNIEnv *env);
+extern int register_android_media_midi(JNIEnv *env);
 
 namespace android {
 
@@ -1441,6 +1442,7 @@
     REG_JNI(register_android_media_MicrophoneInfo),
     REG_JNI(register_android_media_RemoteDisplay),
     REG_JNI(register_android_media_ToneGenerator),
+    REG_JNI(register_android_media_midi),
 
     REG_JNI(register_android_opengl_classes),
     REG_JNI(register_android_server_NetworkManagementSocketTagger),
diff --git a/core/jni/android_media_midi.cpp b/core/jni/android_media_midi.cpp
new file mode 100644
index 0000000..b8af3ead
--- /dev/null
+++ b/core/jni/android_media_midi.cpp
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "NativeMIDI_JNI"
+
+#include <core_jni_helpers.h>
+
+namespace android { namespace midi {
+//  MidiDevice Fields
+static jobject gMidiDeviceClassGlobalRef = nullptr;     // A GlobalRef for MidiDevice Class
+jfieldID gFidMidiNativeHandle = nullptr;         // MidiDevice.mNativeHandle
+jfieldID gFidMidiDeviceServerBinder = nullptr;   // MidiDevice.mDeviceServerBinder
+jfieldID gFidMidiDeviceInfo = nullptr;           // MidiDevice.mDeviceInfo
+
+//  MidiDeviceInfo Fields
+static jobject gMidiDeviceInfoClassGlobalRef = nullptr; // A GlobalRef for MidiDeviceInfoClass
+jfieldID mFidMidiDeviceId = nullptr;             // MidiDeviceInfo.mId
+}}
+
+using namespace android::midi;
+
+int register_android_media_midi(JNIEnv *env) {
+    jclass deviceClass = android::FindClassOrDie(env, "android/media/midi/MidiDevice");
+    gMidiDeviceClassGlobalRef = env->NewGlobalRef(deviceClass);
+
+    // MidiDevice Field IDs
+    gFidMidiNativeHandle = android::GetFieldIDOrDie(env, deviceClass, "mNativeHandle", "J");
+    gFidMidiDeviceServerBinder = android::GetFieldIDOrDie(env, deviceClass,
+            "mDeviceServerBinder", "Landroid/os/IBinder;");
+    gFidMidiDeviceInfo = android::GetFieldIDOrDie(env, deviceClass,
+            "mDeviceInfo", "Landroid/media/midi/MidiDeviceInfo;");
+
+    // MidiDeviceInfo Field IDs
+    jclass deviceInfoClass = android::FindClassOrDie(env, "android/media/midi/MidiDeviceInfo");
+    gMidiDeviceInfoClassGlobalRef = env->NewGlobalRef(deviceInfoClass);
+    mFidMidiDeviceId = android::GetFieldIDOrDie(env, deviceInfoClass, "mId", "I");
+
+    return 0;
+}
diff --git a/media/native/midi/midi.cpp b/media/native/midi/midi.cpp
index a9b498f..78ca0ab 100644
--- a/media/native/midi/midi.cpp
+++ b/media/native/midi/midi.cpp
@@ -87,37 +87,20 @@
 #define AMIDI_PACKET_OVERHEAD   9
 #define AMIDI_BUFFER_SIZE       (AMIDI_PACKET_SIZE - AMIDI_PACKET_OVERHEAD)
 
+// JNI IDs (see android_media_midi.cpp)
+namespace android { namespace midi {
 //  MidiDevice Fields
-static jobject deviceClassGlobalRef = nullptr;     // A GlobalRef for MidiDevice Class
-static jfieldID fidDeviceClosed = nullptr;         // MidiDevice.mIsDeviceClosed
-static jfieldID fidNativeHandle = nullptr;         // MidiDevice.mNativeHandle
-static jfieldID fidDeviceServerBinder = nullptr;   // MidiDevice.mDeviceServerBinder
-static jfieldID fidDeviceInfo = nullptr;           // MidiDevice.mDeviceInfo
+extern jfieldID gFidMidiNativeHandle;         // MidiDevice.mNativeHandle
+extern jfieldID gFidMidiDeviceServerBinder;   // MidiDevice.mDeviceServerBinder
+extern jfieldID gFidMidiDeviceInfo;           // MidiDevice.mDeviceInfo
 
 //  MidiDeviceInfo Fields
-static jobject deviceInfoClassGlobalRef = nullptr; // A GlobalRef for MidiDeviceInfoClass
-static jfieldID fidDeviceId = nullptr;             // MidiDeviceInfo.mId
+extern jfieldID mFidMidiDeviceId;             // MidiDeviceInfo.mId
+}}
+using namespace android::midi;
 
 static std::mutex openMutex; // Ensure that the device can be connected just once to 1 thread
 
-static void AMIDI_initJNI(JNIEnv *env) {
-    jclass deviceClass = android::FindClassOrDie(env, "android/media/midi/MidiDevice");
-    deviceClassGlobalRef = env->NewGlobalRef(deviceClass);
-
-    // MidiDevice Field IDs
-    fidDeviceClosed = android::GetFieldIDOrDie(env, deviceClass, "mIsDeviceClosed", "Z");
-    fidNativeHandle = android::GetFieldIDOrDie(env, deviceClass, "mNativeHandle", "J");
-    fidDeviceServerBinder = android::GetFieldIDOrDie(env, deviceClass,
-            "mDeviceServerBinder", "Landroid/os/IBinder;");
-    fidDeviceInfo = android::GetFieldIDOrDie(env, deviceClass,
-            "mDeviceInfo", "Landroid/media/midi/MidiDeviceInfo;");
-
-    // MidiDeviceInfo Field IDs
-    jclass deviceInfoClass = android::FindClassOrDie(env, "android/media/midi/MidiDeviceInfo");
-    deviceInfoClassGlobalRef = env->NewGlobalRef(deviceInfoClass);
-    fidDeviceId = android::GetFieldIDOrDie(env, deviceInfoClass, "mId", "I");
-}
-
 //// Handy debugging function.
 //static void AMIDI_logBuffer(const uint8_t *data, size_t numBytes) {
 //    for (size_t index = 0; index < numBytes; index++) {
@@ -162,10 +145,6 @@
 media_status_t AMIDI_API AMidiDevice_fromJava(JNIEnv *env, jobject j_midiDeviceObj,
         AMidiDevice** devicePtrPtr)
 {
-    // Ensures JNI initialization is performed just once.
-    static std::once_flag initCallFlag;
-    std::call_once(initCallFlag, AMIDI_initJNI, env);
-
     if (j_midiDeviceObj == nullptr) {
         ALOGE("AMidiDevice_fromJava() invalid MidiDevice object.");
         return AMEDIA_ERROR_INVALID_OBJECT;
@@ -174,13 +153,13 @@
     {
         std::lock_guard<std::mutex> guard(openMutex);
 
-        long handle = env->GetLongField(j_midiDeviceObj, fidNativeHandle);
+        long handle = env->GetLongField(j_midiDeviceObj, gFidMidiNativeHandle);
         if (handle != 0) {
             // Already opened by someone.
             return AMEDIA_ERROR_INVALID_OBJECT;
         }
 
-        jobject serverBinderObj = env->GetObjectField(j_midiDeviceObj, fidDeviceServerBinder);
+        jobject serverBinderObj = env->GetObjectField(j_midiDeviceObj, gFidMidiDeviceServerBinder);
         sp<IBinder> serverBinder = android::ibinderForJavaObject(env, serverBinderObj);
         if (serverBinder.get() == nullptr) {
             ALOGE("AMidiDevice_fromJava couldn't connect to native MIDI server.");
@@ -190,11 +169,11 @@
         // don't check allocation failures, just abort..
         AMidiDevice* devicePtr = new AMidiDevice;
         devicePtr->server = new BpMidiDeviceServer(serverBinder);
-        jobject midiDeviceInfoObj = env->GetObjectField(j_midiDeviceObj, fidDeviceInfo);
-        devicePtr->deviceId = env->GetIntField(midiDeviceInfoObj, fidDeviceId);
+        jobject midiDeviceInfoObj = env->GetObjectField(j_midiDeviceObj, gFidMidiDeviceInfo);
+        devicePtr->deviceId = env->GetIntField(midiDeviceInfoObj, mFidMidiDeviceId);
 
         // Synchronize with the associated Java MidiDevice.
-        env->SetLongField(j_midiDeviceObj, fidNativeHandle, (long)devicePtr);
+        env->SetLongField(j_midiDeviceObj, gFidMidiNativeHandle, (long)devicePtr);
         env->GetJavaVM(&devicePtr->javaVM);
         devicePtr->midiDeviceObj = env->NewGlobalRef(j_midiDeviceObj);
 
@@ -220,17 +199,16 @@
     LOG_ALWAYS_FATAL_IF(err != JNI_OK, "AMidiDevice_release Error accessing JNIEnv err:%d", err);
 
     // Synchronize with the associated Java MidiDevice.
-    // env->CallVoidMethod(j_midiDeviceObj, midClearNativeHandle);
     {
         std::lock_guard<std::mutex> guard(openMutex);
-        long handle = env->GetLongField(device->midiDeviceObj, fidNativeHandle);
+        long handle = env->GetLongField(device->midiDeviceObj, gFidMidiNativeHandle);
         if (handle == 0) {
             // Not opened as native.
             ALOGE("AMidiDevice_release() device not opened in native client.");
             return AMEDIA_ERROR_INVALID_OBJECT;
         }
 
-        env->SetLongField(device->midiDeviceObj, fidNativeHandle, 0L);
+        env->SetLongField(device->midiDeviceObj, gFidMidiNativeHandle, 0L);
     }
     env->DeleteGlobalRef(device->midiDeviceObj);