However, in any case avi to mpeg4 is not equivalent to DVD ripping from a legal standpoint. Because of the DMCA, US law makes a distinction between media that is encrypted for copyright protection purposes and media that is not encrypted. So since DVDs are CSS encrypted and AVIs aren't, the two are covered by somewhat different sets of law.
Obviously an unprotected file has no "means to effectively control access", so copying it should be legal under the DMCA (it's the circumvention that's illegal, not the copying per se). But m4a files are usually DRM'd, so my guess would be that unless a separate determination is made it's still not kosher.