Oh please, do we really have to go through this once every two days? You could have just searched the forum... From here:
The trial versions of Adobe After Effects® CS5, Adobe Premiere® Pro CS5, and Soundbooth® CS5 software do not include some features that depend on software licensed from parties other than Adobe. For example, some codecs for encoding MPEG formats are available only with the full version of these products.
Thanks for your answer.