MediaCodec: don't cache buffers until requested

Bug: 189889230
Test: manual & presubmit
Change-Id: I4caca59d6854416cedb6758fe66aefaacb69beb7

media/java/android/media/MediaCodec.java

@@ -2282,10 +2282,6 @@ final public class MediaCodec {
      */
     public final void start() {
         native_start();
-        synchronized(mBufferLock) {
-            cacheBuffers(true /* input */);
-            cacheBuffers(false /* input */);
-        }
     }
     private native final void native_start();
 
@@ -3916,6 +3912,9 @@ final public class MediaCodec {
                         + "Please obtain MediaCodec.LinearBlock or HardwareBuffer "
                         + "objects and attach to QueueRequest objects.");
             }
+            if (mCachedInputBuffers == null) {
+                cacheBuffers(true /* input */);
+            }
             if (mCachedInputBuffers == null) {
                 throw new IllegalStateException();
             }
@@ -3954,6 +3953,9 @@ final public class MediaCodec {
                         + "is not compatible with CONFIGURE_FLAG_USE_BLOCK_MODEL. "
                         + "Please use getOutputFrame to get output frames.");
             }
+            if (mCachedOutputBuffers == null) {
+                cacheBuffers(false /* input */);
+            }
             if (mCachedOutputBuffers == null) {
                 throw new IllegalStateException();
             }