No audio in Mpeg2

But is it realy true that you can´t play audio from Mpeg2 made in Compressor 3.0.5?

If by "play" you mean in the QT Player, then "yes" or "no" as the conditions may be. QT does not play multiplexed AC3 or PCM audio. Further, even if AC3 audio and your MPEG-2 video content is stored as elementary streams, it cannot be played by the QT Player "natively."

Since you did not indicate how your "MPEG-2" files were encoded by Compressor 3.0.5, I cannot specify which method of playing your content would be best here without knowing if the contents is multiplexed or not, whether it contains AC3 you want supported in 5.1, or which applications you might prefer/have available.

I´ve tryed VLC palyer now, it works, but it would be easyer if QT would play it.

Then you have a number of options. Basically, they all amount to encoding the files so that they can be played in a QT Player. For instance MPEG-2 video content "muxed" with MPEG-1, Layer 1/2 audio would be playable in a QT Player assuming you have the Apple MPEG-2 Playback component installed. This would likely be the simplest approach directly from Compressor. However, again assuming you have the MPEG-2 Playback component installed, you can use the free MPEG Streamclip app to "remux" your current MPEG2/AC3 (or other muxed audio) content directly to MPEG2/MP2 files without having to re-encode the original data with Compressor. The resulting files would be compatible with QT 7 Player, QT X Player, VLC, MPEG Streamclip, as well as, various other players and converter/player apps. However, remember that the MPEG file container retains its file size limitation for whatever system/player you are using. For really long files, you would be better off creating DVD VIDEO_TS folders and playing the content with Apple DVD Player, Front Row, VLC, MPEG Streamclip, or similar players.