Free copyright music is illegal, without the artists approval.
That violates the copyright laws
and asking that question violates yahoos guidelines.
"Violating the law
Members of Yahoo! Answers are not above the law, so don't post anything that violates the laws of your country, state, province, or city. Don't try to trick people into sharing their personal information, steal anything (like copyright or trademark material),"
While it is legal to watch youtube, it is NOT legal to download copyright music from there.
Yahoo knows this, and that's why they do NOT have their own download button, on the site.
You have to get the software to steal the music from another site.