Although ht5streamer is completely immature and relatively incomplete yet, it shows great simplicity and functionality in what it does. You can currently search and view videos and playlists from YouTube or Dailymotion, browse suggested videos and watch them in full screen, download the videos in all possible/available qualities and finally convert them to mp3s!
Not exactly feature-galore, but this is version 0.1 and what little ht5streamer does it does well and with general stability. What I usually like to work with for such tasks is Minitube which is a great application, but it does have a lot of issues with frequent instability and lack of enough download options, as well as the complete lack of any other service other than YouTube.
This configuration init screen that you can open anytime is basically all the options you can set (for now)
Searching is fast and supports sorting and filters (HD,3D). Double clicking the results on the left plays the video on the right
Possible/available video quality for download is displayed accordingly
Downloading begins when clicking a quality option. A progress bar with the percentage and speed is displayed
After the download is complete, you can convert the downloaded file to mp3 with the pressing of a mouse click
To use ht5streamer you won’t have to install anything at all as binaries are included in the downloaded file. Also, this app is available for both 32 and 64-bit platforms. An Ubuntu ppa will be available soon. For more info about how to install and use this tool, and how you can make it read mp4 files go ahead and visit the download webpage.