Here is a useful Mac Video grabber called Get Tube – A free Youtube downloader for Mac OSX which downloads and convert Youtube videos into audio file format and saves them in .mp3 and .mp4 extension.You can also select m4a file name for downloading the full video in .m4a extension.

The latest version of Get Tube 3.0 is available for Mac OS 10.5 Leopard or later,if you are using Mac OS 10.4 then download Get tube 2.3 version which works perfectly and downloads youtube videos quite easily.Overall Get tube is a easy youtube mp3 converter and downloader as it adds flexibility to download and extract only audio songs from youtube.

Download GetTube v.3.0 For Mac OSX 10.5 or later

Download GetTube v.2.3a For Mac OSX 10.4

Here is a video explaining how to use Get tube on MAC to download and convert youtube videos into mp3 or mp4 files.