Impress- not hearing mp3

Put mp3 audio file to my impress presentation, but there is nothing to hear!
What way to do it: insert music and video, OR task. slide trans. ???

One pages say first, other say second(+ disable insert music and vide- how???).

Many thanks!

With Linux you need to install the libreoffice-avmedia-backend-gstreamer
In Windows 7 I had to install a codec package called K-Lite_Codec_Pack_955_Basic.exe
In Ubuntu 12.04 audio works OK, but in later versions I have problems with a bug that creates a 10 second freeze before audio starts playing. In Windows 7 my current LibreOffice 4.4 works OK, on Ubuntu 12.04 I even have LibreOffice 5.0 and that works OK too. In Ubuntu 14.04 and Mint Mate 17.x I have the delay-bug for which I still hope someone will find the cause…

Cheers, Peter