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There used to be an Amarok plugin to search and add youtube videos to your playlist that made use of some website to fetch the URL for the .flv from the youtube page. It never worked for me, and is no longer supported.

Could something similar be made which made use of the program youtube-dl offered by most distributions to get the .flv? Rather than polling some random website, it would make a lot of sense to have that work done locally. It would have this program youtube-dl as a dependency, but that wouldn't be very different from other scripts that have ruby or python as dependencies.

youtube-pl is a small Python-Script with some modifications and ffmpeg you can easily get the songs in mp3 format.
It's very simple: Download it and invoke ffmpeg.

There's a built in in 2.2git but there doesn't seem any way to do a custom search, modify the search that Amarok creates for that particular song or bookmark the video. But this is probably a work in process and will change over time.

From pytube you could get code for searching videos.