看看类的最后一部分(335-442行),转换Runnable对象只是做这个工作！您必须根据需要调整代码,调整输入和输出文件路径以及转换参数(采样率,比特率等).

public static final String AUdio_RECORDING_FILE_NAME = "audio_Capturing-190814-034638.422.wav"; // Input PCM file
public static final String COMPRESSED_AUdio_FILE_NAME = "convertedmp4.m4a"; // Output MP4/M4A file
public static final String COMPRESSED_AUdio_FILE_MIME_TYPE = "audio/mp4a-latm";
public static final int COMPRESSED_AUdio_FILE_BIT_RATE = 64000; // 64kbps
public static final int SAMPLING_RATE = 48000;
public static final int BUFFER_SIZE = 48000;
public static final int CODEC_TIMEOUT_IN_MS = 5000;
String LOGTAG = "CONVERT AUdio";
Runnable convert = new Runnable() {
    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
    @Override
    public void run() {
        android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);
        try {
            String filePath = Environment.getExternalStorageDirectory().getPath() + "/" + AUdio_RECORDING_FILE_NAME;
            File inputFile = new File(filePath);
            FileInputStream fis = new FileInputStream(inputFile);

            File outputFile = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/" + COMPRESSED_AUdio_FILE_NAME);
            if (outputFile.exists()) outputFile.delete();

            MediaMuxer mux = new MediaMuxer(outputFile.getAbsolutePath(),MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);

            MediaFormat outputFormat = MediaFormat.createAudioFormat(COMPRESSED_AUdio_FILE_MIME_TYPE,SAMPLING_RATE,1);
            outputFormat.setInteger(MediaFormat.KEY_AAC_PROFILE,MediaCodecInfo.CodecProfileLevel.AACObjectLC);
            outputFormat.setInteger(MediaFormat.KEY_BIT_RATE,COMPRESSED_AUdio_FILE_BIT_RATE);
            outputFormat.setInteger(MediaFormat.KEY_MAX_INPUT_SIZE,16384);

            MediaCodec codec = MediaCodec.createEncoderByType(COMPRESSED_AUdio_FILE_MIME_TYPE);
            codec.configure(outputFormat,null,MediaCodec.CONFIGURE_FLAG_ENCODE);
            codec.start();

            ByteBuffer[] codecInputBuffers = codec.getInputBuffers(); // Note: Array of buffers
            ByteBuffer[] codecOutputBuffers = codec.getOutputBuffers();

            MediaCodec.BufferInfo outBuffInfo = new MediaCodec.BufferInfo();
            byte[] tempBuffer = new byte[BUFFER_SIZE];
            boolean hasMoreData = true;
            double presentationTimeUs = 0;
            int audioTrackIdx = 0;
            int totalBytesRead = 0;
            int percentComplete = 0;
            do {
                int inputBufIndex = 0;
                while (inputBufIndex != -1 && hasMoreData) {
                    inputBufIndex = codec.dequeueInputBuffer(CODEC_TIMEOUT_IN_MS);

                    if (inputBufIndex >= 0) {
                        ByteBuffer dstBuf = codecInputBuffers[inputBufIndex];
                        dstBuf.clear();

                        int bytesRead = fis.read(tempBuffer,dstBuf.limit());
                        Log.e("bytesRead","Readed "+bytesRead);
                        if (bytesRead == -1) { // -1 implies EOS
                            hasMoreData = false;
                            codec.queueInputBuffer(inputBufIndex,(long) presentationTimeUs,MediaCodec.BUFFER_FLAG_END_OF_STREAM);
                        } else {
                            totalBytesRead += bytesRead;
                            dstBuf.put(tempBuffer,bytesRead);
                            codec.queueInputBuffer(inputBufIndex,bytesRead,0);
                            presentationTimeUs = 1000000l * (totalBytesRead / 2) / SAMPLING_RATE;
                        }
                    }
                }
                // Drain audio
                int outputBufIndex = 0;
                while (outputBufIndex != MediaCodec.INFO_TRY_AGAIN_LATER) {
                    outputBufIndex = codec.dequeueOutputBuffer(outBuffInfo,CODEC_TIMEOUT_IN_MS);
                    if (outputBufIndex >= 0) {
                        ByteBuffer encodedData = codecOutputBuffers[outputBufIndex];
                        encodedData.position(outBuffInfo.offset);
                        encodedData.limit(outBuffInfo.offset + outBuffInfo.size);
                        if ((outBuffInfo.flags & MediaCodec.BUFFER_FLAG_CODEC_CONFIG) != 0 && outBuffInfo.size != 0) {
                            codec.releaSEOutputBuffer(outputBufIndex,false);
                        }else{
                            mux.writeSampleData(audioTrackIdx,codecOutputBuffers[outputBufIndex],outBuffInfo);
                            codec.releaSEOutputBuffer(outputBufIndex,false);
                        }
                    } else if (outputBufIndex == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
                        outputFormat = codec.getOutputFormat();
                        Log.v(LOGTAG,"Output format changed - " + outputFormat);
                        audioTrackIdx = mux.addTrack(outputFormat);
                        mux.start();
                    } else if (outputBufIndex == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
                        Log.e(LOGTAG,"Output buffers changed during encode!");
                    } else if (outputBufIndex == MediaCodec.INFO_TRY_AGAIN_LATER) {
                        // NO OP
                    } else {
                        Log.e(LOGTAG,"Unknown return code from dequeueOutputBuffer - " + outputBufIndex);
                    }
                }
                percentComplete = (int) Math.round(((float) totalBytesRead / (float) inputFile.length()) * 100.0);
                Log.v(LOGTAG,"Conversion % - " + percentComplete);
            } while (outBuffInfo.flags != MediaCodec.BUFFER_FLAG_END_OF_STREAM);
            fis.close();
            mux.stop();
            mux.release();
            Log.v(LOGTAG,"Compression done ...");
        } catch (FileNotFoundException e) {
            Log.e(LOGTAG,"File not found!",e);
        } catch (IOException e) {
            Log.e(LOGTAG,"IO exception!",e);
        }

        //mStop = false;
        // Notify UI thread...
    }
};