MP3 converters that support YouTube as a source are common, despite the sometimes vague laws that apply (see the "Copyright and Private Copies" box). The names of these tools are often quite similar and among them are a few online services, such as Filsh.net, Convert2mp3.net, and Youtube-mp3.org. You can even get Firefox plugins that do the job [1].

Among native converters is the very popular and free (as in beer) YouTube to MP3 Converter [2], which Ubuntu users can find in the Ubuntu Software Center. From there, you can easily install before going through the Ubuntu One payment platform (Figure 1). Note that the software is proprietary and, although you are forced through the U1 payment platform, you are not charged anything.

Why the tool appears in Software Center as purchasable, when it is actually free, is not clear. In any case, if you are not comfortable going through the payment process (to end up not paying anything), you can always install the tool directly from the manufacturer's website [3].

[...]