我最近尝试用yt-dlp批量下载YouTube视频，结果碰到了棘手的问题：下载好的视频完全没有声音，明显是音视频没合并成功，而且脚本运行时还抛出了__files_to_merge的错误。

我自己写了一段Python脚本，实在找不到问题出在哪，想请各位帮忙看看怎么调整才能让音视频正常合并，下载出有完整声音的视频？

错误提示内容：

Error: '__files_to_merge'

我的代码如下：

import os
import yt_dlp

def download_video(video_url, save_path):
    if not save_path.endswith('.mp4'):
        save_path += '.mp4'

    try:
        ydl_opts = {
            'outtmpl': save_path,
            'format': 'bestvideo+bestaudio/best',
            'merge_output_format': 'mp4',
            'postprocessors': [
                {'key': 'FFmpegMerger'},
            ],
        }
        with yt_dlp.YoutubeDL(ydl_opts) as ydl:
            ydl.download([video_url])
        print(f"Downloaded: {save_path}")
    except Exception as e:
        print(f"Failed to download: {video_url}\nError: {e}")

def main():
    # List of video URLs
    video_urls = [
        'https://youtu.be/u_CQggTmSO8',  # Example URL
        'https://youtu.be/vCzMfZtrdjk',
        # Add more video URLs here
    ]

    # Directory to save videos
    save_dir = 'Udacity_GenAI_Videos'
    if not os.path.exists(save_dir):
        os.makedirs(save_dir)

    for i, video_url in enumerate(video_urls):
        save_path = os.path.join(save_dir, f'video_{i+1}.mp4')
        download_video(video_url, save_path)

if __name__ == "__main__":
    main()

备注：内容来源于stack exchange，提问作者Kaleab Woldemariam