Use getExternalStorageDirectory() for trace file.

webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java

 /*
  *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 package org.appspot.apprtc;
 
 import android.content.Context;
 import android.os.ParcelFileDescriptor;
+import android.os.Environment;
 import android.util.Log;
 
 import org.appspot.apprtc.AppRTCClient.SignalingParameters;
 import org.appspot.apprtc.util.LooperExecutor;
 import org.webrtc.CameraEnumerationAndroid;
 import org.webrtc.DataChannel;
 import org.webrtc.EglBase;
 import org.webrtc.IceCandidate;
 import org.webrtc.Logging;
 import org.webrtc.MediaCodecVideoEncoder;
@@ skipping 261 matching lines @@
     });
   }
 
   public boolean isVideoCallEnabled() {
     return videoCallEnabled;
   }
 
   private void createPeerConnectionFactoryInternal(Context context) {
       PeerConnectionFactory.initializeInternalTracer();
       if (peerConnectionParameters.tracing) {
-          PeerConnectionFactory.startInternalTracingCapture("/mnt/sdcard/webrtc-trace.txt");
+          PeerConnectionFactory.startInternalTracingCapture(
+                  Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator
+                  + "webrtc-trace.txt");
       }
     Log.d(TAG, "Create peer connection factory. Use video: " +
         peerConnectionParameters.videoCallEnabled);
     isError = false;
 
     // Initialize field trials.
     PeerConnectionFactory.initializeFieldTrials(FIELD_TRIAL_AUTOMATIC_RESIZE);
 
     // Check preferred video codec.
     preferredVideoCodec = VIDEO_CODEC_VP8;
@@ skipping 767 matching lines @@
     public void onCreateFailure(final String error) {
       reportError("createSDP error: " + error);
     }
 
     @Override
     public void onSetFailure(final String error) {
       reportError("setSDP error: " + error);
     }
   }
 }