songOutPath = Environment.getExternalStorageDirectory()+"/My Folder/song.mp4";
            muxer = new MediaMuxer(songOutPath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);
            mTrackIndex = muxer.addTrack(format);
            muxer.start();
            mMuxerStarted = true;

            MediaCodec.BufferInfo info = new MediaCodec.BufferInfo();
            final long timeoutUs = 5000;
            boolean sawInputEOS = false;
            boolean sawOutputEOS = false;
            int noOutputCounter = 0;

            MediaCodec.BufferInfo info2 = new MediaCodec.BufferInfo();
            final long timeoutUs2 = 5000;
            boolean sawInputEOS2 = false;
            boolean sawOutputEOS2 = false;
            int noOutputCounter2 = 0;

            while (!sawOutputEOS && !sawOutputEOS2 && noOutputCounter < 50 && noOutputCounter2 < 50) {
                noOutputCounter++;
                if (!sawInputEOS) {
                    int inputBufferIndex = codec.dequeueInputBuffer(timeoutUs);
                    if (inputBufferIndex >= 0) {
                        ByteBuffer buffer = codecInputBuffers[inputBufferIndex];
                        int sampleSize = extractor.readSampleData(buffer, 0);
                        long presentationTimeUs = 0;
                        if (sampleSize < 0) {
                            sawInputEOS = true;
                            sampleSize = 0;
                        } else {
                            presentationTimeUs = extractor.getSampleTime();
                        }
                        codec.queueInputBuffer(inputBufferIndex, 0, sampleSize,
                                presentationTimeUs,
                                sawInputEOS ? MediaCodec.BUFFER_FLAG_END_OF_STREAM : 0);
                        if (!sawInputEOS) {
                            extractor.advance();
                        }
                    }
                }
                noOutputCounter2++;
                if (!sawInputEOS2) {
                    int inputBufferIndex2 = codec2.dequeueInputBuffer(timeoutUs2);
                    if (inputBufferIndex2 >= 0) {
                        ByteBuffer buffer2 = codecInputBuffers2[inputBufferIndex2];
                        int sampleSize2 = extractor2.readSampleData(buffer2, 0);
                        long presentationTimeUs2 = 0;
                        if (sampleSize2 < 0) {
                            sawInputEOS2 = true;
                            sampleSize2 = 0;
                        } else {
                            presentationTimeUs2 = extractor2.getSampleTime();
                        }
                        codec2.queueInputBuffer(inputBufferIndex2, 0, sampleSize2,
                                presentationTimeUs2,
                                sawInputEOS2 ? MediaCodec.BUFFER_FLAG_END_OF_STREAM : 0);
                        if (!sawInputEOS2) {
                            extractor2.advance();
                        }
                    }
                }

                int outputBufferIndex = codec.dequeueOutputBuffer(info, timeoutUs);
                int outputBufferIndex2 = codec2.dequeueOutputBuffer(info2, timeoutUs2);
                if (outputBufferIndex >= 0) {
                    if (info.size > 0) {
                        noOutputCounter = 0;
                    }
                    if (info2.size > 0) {
                        noOutputCounter2 = 0;
                    }
                    ByteBuffer buffer = codecOutputBuffers[outputBufferIndex];
                    ByteBuffer buffer2 = codecOutputBuffers2[outputBufferIndex2];

                    shortArrayOne = new short[info.size/2];
                    shortArrayTwo = new short[info2.size/2];

                    buffer.order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().get(shortArrayOne);
                    buffer.clear();
                    buffer2.order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().get(shortArrayTwo);
                    buffer2.clear();

                    shortArrayThree = mix(shortArrayOne, shortArrayTwo);
                    if(shortArrayThree.length > 0){
                        //audioTrack.write(shortArrayThree,0,shortArrayThree.length);
                        ByteBuffer byteBuf = ByteBuffer.allocate(2*shortArrayThree.length);
                        int index;
                        for(index = 0; index != shortArrayThree.length; index++)
                        {
                            byteBuf.putShort(shortArrayThree[index]);
                        }
                        muxer.writeSampleData(mTrackIndex, byteBuf, info);
                    }

                    codec.releaseOutputBuffer(outputBufferIndex, false);
                    codec2.releaseOutputBuffer(outputBufferIndex2, false);
                    if ((info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
                        sawOutputEOS = true;
                    }
                    if ((info2.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
                        sawOutputEOS2 = true;
                    }
                } else if (outputBufferIndex == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
                    codecOutputBuffers = codec.getOutputBuffers();
                    if (outputBufferIndex2 == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
                        codecOutputBuffers2 = codec2.getOutputBuffers();
                    }
                }
            }