一、步骤分为以下几步

1：申请读写外置卡权限

2：使用MediaProjectionManager进行屏幕录制

3：使用MediaCodec进行编码

4：保存到外置卡

二、代码实现

1：申请权限，首先在AndroidManifest.xml文件中加入权限声明，其次使用下面代码申请权限

  public boolean checkPermission() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && checkSelfPermission(
                Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(new String[]{
                    Manifest.permission.READ_EXTERNAL_STORAGE,
                    Manifest.permission.WRITE_EXTERNAL_STORAGE
            }, 1);

        }
        return false;
    }

2：获取MediaProjectionManager服务，发起录屏请求

MediaProjectionManager  mediaProjectionManager = (MediaProjectionManager)   getSystemService(Context.MEDIA_PROJECTION_SERVICE);
Intent captureIntent = mediaProjectionManager.createScreenCaptureIntent();
startActivityForResult(captureIntent,100);

请求结果在onActivityResult方法中回调

  @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == 100 && resultCode == Activity.RESULT_OK) {
            mediaProjection = mediaProjectionManager.getMediaProjection
                    (resultCode, data);
            initMediaCodec();

        }
    }

3：编码数据

  private void initMediaCodec() {
        try {
            //创建H264编码对象，H264传入video/avc，H265传入video/hevc
            mediaCodec = MediaCodec.createEncoderByType("video/avc");
            //视频信息配置
            MediaFormat format = MediaFormat.createVideoFormat(MediaFormat.MIMETYPE_VIDEO_AVC, 540, 960);
            //颜色
            format.setInteger(MediaFormat.KEY_COLOR_FORMAT, MediaCodecInfo.CodecCapabilities.COLOR_FormatSurface);
            format.setInteger(MediaFormat.KEY_FRAME_RATE,15);//帧数
            format.setInteger(MediaFormat.KEY_BIT_RATE,400000);//比特率
            format.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL,2);//i帧间隔
            //设置配置信息给mediaCodec
            mediaCodec.configure(format,null,null,MediaCodec.CONFIGURE_FLAG_ENCODE);
            final Surface surface = mediaCodec.createInputSurface();
            new Thread(){
                @Override
                public void run() {
                   mediaCodec.start();
                   mediaProjection.createVirtualDisplay("screen-codec",
                           540,960,1,
                           DisplayManager.VIRTUAL_DISPLAY_FLAG_PUBLIC,
                           surface,null,null);
                    MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
                    while (true){
                        //获取可用ByteBuffer下标
                        int index = mediaCodec.dequeueOutputBuffer(bufferInfo, 100000);
                        if(index>0){
                            ByteBuffer buffer = mediaCodec.getOutputBuffer(index);
                            byte[] outData=new byte[bufferInfo.size];
                            //给outData设置数据
                            buffer.get(outData);
                            //写入文件
                            writeContent(outData);
                            //释放资源
                            mediaCodec.releaseOutputBuffer(index,false);

                        }
                    }
                }
            }.start();

        } catch (IOException e) {
            e.printStackTrace();
        }


    }

4：写入外置卡

 public   String writeContent(byte[] array) {
        char[] HEX_CHAR_TABLE = {
                '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
        };
        StringBuilder sb = new StringBuilder();
        for (byte b : array) {
            sb.append(HEX_CHAR_TABLE[(b & 0xf0) >> 4]);
            sb.append(HEX_CHAR_TABLE[b & 0x0f]);
        }
        FileWriter writer = null;
        try {
          
            writer = new FileWriter(Environment.getExternalStorageDirectory()+"/result.txt", true);
            writer.write(sb.toString());
            writer.write("\n");
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if(writer != null){
                    writer.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return sb.toString();
    }

最终输出结果