Clean up the native code to match Java update

1. Add flags to match the java side change.
2. Update the interface.

bug:7991013

Change-Id: I8ffe84c466b2a68e2e1e48b35b78db9e44640265
diff --git a/cmds/stagefright/muxer.cpp b/cmds/stagefright/muxer.cpp
index 1b127c7..fac2acc 100644
--- a/cmds/stagefright/muxer.cpp
+++ b/cmds/stagefright/muxer.cpp
@@ -69,7 +69,8 @@
     ALOGV("input file %s, output file %s", path, outputFileName);
     ALOGV("useAudio %d, useVideo %d", useAudio, useVideo);
 
-    sp<MediaMuxer> muxer = new MediaMuxer(outputFileName);
+    sp<MediaMuxer> muxer = new MediaMuxer(outputFileName,
+                                          MediaMuxer::OUTPUT_FORMAT_MPEG_4);
 
     size_t trackCount = extractor->countTracks();
     // Map the extractor's track index to the muxer's track index.