如何在ListView适配器中从视频地址加载视频缩略图

public class VideoListAdapter extends BaseAdapter {
    private Context mContext;
    private List<String> mVideoList;

    public VideoListAdapter(Context context, List<String> videoList) {
        mContext = context;
        mVideoList = videoList;
    }

    @Override
    public int getCount() {
        return mVideoList.size();
    }

    @Override
    public Object getItem(int position) {
        return mVideoList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;

        if (convertView == null) {
            convertView = LayoutInflater.from(mContext).inflate(R.layout.list_item_video, parent, false);
            holder = new ViewHolder();
            holder.thumbnailImageView = convertView.findViewById(R.id.thumbnail_image_view);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        String videoUrl = mVideoList.get(position);

        // 设置默认缩略图
        holder.thumbnailImageView.setImageResource(R.drawable.default_thumbnail);

        // 异步加载缩略图
        LoadThumbnailTask task = new LoadThumbnailTask(holder.thumbnailImageView);
        task.execute(videoUrl);

        return convertView;
    }

    private static class ViewHolder {
        ImageView thumbnailImageView;
    }

    private class LoadThumbnailTask extends AsyncTask<String, Void, Bitmap> {
        private ImageView mImageView;

        public LoadThumbnailTask(ImageView imageView) {
            mImageView = imageView;
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            String videoUrl = params[0];
            Bitmap thumbnail = null;

            try {
                MediaMetadataRetriever retriever = new MediaMetadataRetriever();
                retriever.setDataSource(videoUrl);
                thumbnail = retriever.getFrameAtTime();
                retriever.release();
            } catch (Exception e) {
                e.printStackTrace();
            }

            return thumbnail;
        }

        @Override
        protected void onPostExecute(Bitmap thumbnail) {
            if (thumbnail != null) {
                mImageView.setImageBitmap(thumbnail);
            }
        }
    }
}