文件拷贝涉及到sd卡的读写，所有需要在配置文件中添加读写权限。因为没有使用动态权限，此方法仅限于，targetSdkVersion小于等于22的项目。

   public String copyVideoToSD(Context context, String fileName) {
       String path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath() + "/" + getPackageName() + "/";
       InputStream inputStream;
       try {
           //判断文件是否存在
           File file1 = new File(path + "/" + fileName);
           if (!file1.exists()) {
               Toast.makeText(context, "正在处理", Toast.LENGTH_LONG).show();
               inputStream = getAssets().open(fileName);
               File file = new File(path);
               //当目录不存在时创建目录
               if (!file.exists()) {
                   file.mkdirs();
               }
               FileOutputStream fileOutputStream = new FileOutputStream(path + "/" + fileName);// 保存到本地的文件夹下的文件
               byte[] buffer = new byte[1024];
               int count = 0;
               while ((count = inputStream.read(buffer)) > 0) {
                   fileOutputStream.write(buffer, 0, count);
               }
               fileOutputStream.flush();
               fileOutputStream.close();
               inputStream.close();
           } else {
               Toast.makeText(context, "已存在", Toast.LENGTH_LONG).show();
           }
           return path + fileName;
       } catch (IOException e) {
           e.printStackTrace();
           return "";
       }
   }

//获取到拷贝后的视频播放地址
String path_url=copyVideoToSD("xxx.mp4");
//其他地方使用播放地址
String path_url2 =
Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath() + "/{包名}/xxx.mp4";