youtube video downloaded successfully on local, but on server(online) only 0 byte flv is downloading

should help you out The issue is the output which is returned from youtube-dl is several lines of information, so ffmpeg doesn't know how to deal with it properly.
You'll want to return the actual name of the file without any other information included; a tool like awk or sed can be helpful for this. In addition there will need to be an encoding step added at the end so the audio stream gets copied to the output file (libmp3lame->mp3).

To fix the issue you can do You'll have to use the static YoutubeDL.getVideoInfo(String url)-method. Afterwards you can either save it into a VideoInfo-instance or use the member variable directly from the return value.

To fix this issue If you have direct link to the video itself, like http://www.dl.com/xxx.mp4, you can direct use ffprobe to get the duration of this video by using:

I wish this helpful for you Node.js web servers do not serve directories unless you explicitly tell them to.
If you're using Express, use the static() middleware to tell it to serve that directory.

With these it helps Sergiy Shcherbina's answer helped me solve this issue. I was running my web server from a vm and accessing it through my local IP address.
It seems that you need to access your page that contains the embedded youtube player through a host name and NOT an IP address.