Support Android API 19

Since "adb forward" fallback has been implemented, it is easy to support
API 19.

Replace the incompatible calls related to MediaCodec to use
minSdkVersion 19 instead of 21.

README.md

@@ -9,7 +9,7 @@ and _MacOS_.
 
 ## Requirements
 
-The Android part requires at least API 21 (Android 5.0).
+The Android part requires at least API 19 (Android 4.4).
 
 You need [adb]. It is available in the [Android SDK platform
 tools][platform-tools], or packaged in your distribution (`android-adb-tools`).

server/build.gradle

@@ -4,7 +4,7 @@ android {
     compileSdkVersion 27
     defaultConfig {
         applicationId "com.genymobile.scrcpy"
-        minSdkVersion 21
+        minSdkVersion 19
         targetSdkVersion 27
         versionCode 2
         versionName "1.1"

server/src/main/java/com/genymobile/scrcpy/ScreenEncoder.java

@@ -6,6 +6,7 @@ import android.graphics.Rect;
 import android.media.MediaCodec;
 import android.media.MediaCodecInfo;
 import android.media.MediaFormat;
+import android.os.Build;
 import android.os.IBinder;
 import android.view.Surface;
 
@@ -77,11 +78,17 @@ public class ScreenEncoder implements Device.RotationListener {
         }
     }
 
+    @SuppressWarnings("deprecation") // Android API 19 requires to call deprecated methods
     private boolean encode(MediaCodec codec, OutputStream outputStream) throws IOException {
         @SuppressWarnings("checkstyle:MagicNumber")
         byte[] buf = new byte[bitRate / 8]; // may contain up to 1 second of video
         boolean eof = false;
         MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
+
+        ByteBuffer[] outputBuffers = null;
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
+            outputBuffers = codec.getOutputBuffers();
+        }
         while (!consumeRotationChange() && !eof) {
             int outputBufferId = codec.dequeueOutputBuffer(bufferInfo, -1);
             eof = (bufferInfo.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0;
@@ -91,7 +98,12 @@ public class ScreenEncoder implements Device.RotationListener {
                     break;
                 }
                 if (outputBufferId >= 0) {
-                    ByteBuffer outputBuffer = codec.getOutputBuffer(outputBufferId);
+                    ByteBuffer outputBuffer;
+                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+                        outputBuffer = codec.getOutputBuffer(outputBufferId);
+                    } else {
+                        outputBuffer = outputBuffers[outputBufferId];
+                    }
                     while (outputBuffer.hasRemaining()) {
                         int remaining = outputBuffer.remaining();
                         int len = Math.min(buf.length, remaining);
@@ -100,6 +112,8 @@ public class ScreenEncoder implements Device.RotationListener {
                         outputBuffer.get(buf, 0, len);
                         outputStream.write(buf, 0, len);
                     }
+                } else if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP && outputBufferId == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
+                    outputBuffers = codec.getOutputBuffers();
                 }
             } finally {
                 if (outputBufferId >= 0) {