检查是否正确设置文件路径和是否有写入存储的权限。可以使用以下代码作为参考：

// 检查是否有写入存储的权限
if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
        != PackageManager.PERMISSION_GRANTED) {
    // 没有权限，则请求权限
    ActivityCompat.requestPermissions(this,
            new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
            MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE);
} else {
    // 有权限则保存视频
    saveVideo();
}

// 保存视频到指定路径
private void saveVideo() {
    String folderName = "MyVideos";
    String fileName = "MyVideo.mp4";
    String filePath = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES) + "/" + folderName + "/" + fileName;

    // 确保文件夹存在
    File folder = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES), folderName);
    if (!folder.exists()) {
        folder.mkdirs();
    }

    // 保存视频
    File file = new File(filePath);
    try {
        FileOutputStream fos = new FileOutputStream(file);
        // 写入视频数据
        fos.write(videoData);
        fos.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

其中，MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE是请求存储权限时用到的请求码，videoData是视频数据。