video and audio downloader

Hello! I am editing videos for my YouTube channel by downloading and converting videos in MP3 and MP4 formats. I can't find a good website for downloading. Either the download is very slow, the website is overwhelmed with ads, or there are errors during downloading – sometimes it doesn't work at all. Especially downloading copyrighted videos is very difficult. I want to download videos not only from YouTube but also from other platforms, and I don't want to deal with this separately. Even though I use a download manager, it doesn't download all the videos and errors occur. Do you know of one or more reliable websites that fulfill all these requirements? Thank you in advance!