Question: how to download all videos from youtube playlist using idm?
Answer:  Launch Your Web browser, Go to YouTube, get or copy the link (URL) of playlist to download.
 Go to YouTube Multi Downloader.
 On the top right, click on playlist.
 A YouTube Playlist downloader will appear, select format for the download, For example mp4 360p, MP4 720p, MP3 1080p and other formats available.