When you receive an audio file as an email attachment, click the play button and Google will play the audio file for you in a popup window.
Very neat implementation (see screenshot)
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Now digging into the GMail Mp3 player code, I discovered that it's actually the Google video player that's playing the audio file.
Infact, you can play any MP3 files from the embedded Google Video player without even having to login to GMail. Here's the secret URL (works perfect in Firefox)
http://mail.google.com/mail/html/audio. ... rl=MP3_URL
Replace the MP3_URL with the actual location of the MP3 file on the web and play it inside Google Video. Odeo, take note. Google is entering your territory.
Bron : Labnol Blog
Meer info : Google System Blog