Quicktime X with OSX10.7 won't playback ac-3

Have you any experience with this?

No, not your problems.

I installed Quicktime Pro 7.7, but that won't accept the mpeg2 plugin, because that won't install later than OSX 10.6.

If by "Quicktime Pro 7.7 you are referring to the current v7.7.1 QT structure embeded in the Lion OS and the QT Player 7 v7.6.6 keyed for pro use, then the current QT MPEG-2 Playback component is still compatible but must be installed using the MPEG Streamclip beta installer utility, Pacifist, or be manually transferred from an older OS platform on which the Apple "Installer.app" was used to install the component. (For QT 7 playback I would normally demux the "muxed" MPEG-2 video to an M2V elementary stream paired with an AIFF audio elementary stream.)

I have an mpeg2 file with ac-3 that I played back on a mac mini, OSX 10.7. Worked fine in the test. Surround went to decoder and everything looked peachy. When I went to install the computer the file wouldn't play, or pass the ac-3 to the decoder. Quicktime says the codec isn't recognizable.

Muxed MPEG-2/AC3 content should be compatible with the QT X Player under Lion in MPG, MPEG, and TS file containers but is not supported with VOB or MOV file extensions. However, playback can vary dramaticly depending on media player, system configuration, and actual content. (I would normally use VLC for DD5.1 "passthrough" playback via an external decoder/amplifier.)

I was able to get ac-3 to pass through to the decoder over toslink by encoding the file as a dvd and using DVD player, with prefs set to Digital Audio Output on the audio output, to play back the file from the VideoTS folder.

Yes, the Apple DVD Player supports "passthrough" on all current Leopard, Snow Leopard, and Lion OS platforms.

I can play back the m2v file with quicktime, but the ac-3 file returns that the codec is not avaiable.

Elementary stream automatic paired playback is supported by QT 7 only. QT X requires both files be manually loaded and simultaneously started for playbaclk leaving the possibility of sync problems for long files. AC3 is natively supported by QT only under Lion OS when in an acceptable file container/extension. You could try demuxing VOB content to MPEG-2/MP2 files which would be supported by QT X and QT 7 w/MPEG-2 component or simply use the DVD player.

The reason we wanted to use Quicktime Player Pro is so we could have full screen playback with no on screen controls. All the other players have on screen controls that distract from the auditorium experience of this program.

Not sure what you really want here. All players—QT 7, QT X, VLC, DVD Player (with Quartz Extreme)—have disappearing controls and borderless playback in the "Full Screen" mode. Even the QT 7 Pro Player with the "None Player Controller" property set employs a disappearing controller in the "Full Screen" mode.

I don't want a disappearing controller. I want no controller at all. I will use keyboard shortcuts to play, I don't want a controller showing in a theater environment.

You appear to have two main problems here. The first is that you seem to have very specific playback requirements but you are doling them out piecemeal and often in a misleading manner. The second is that you have not really revealed exactly what your goals are here.

If you actually have QT 7 Pro installed and want to play the file using a "QT Player app" in a "full screen" mode with no "disappearing" controls using media sourced from DVD media content, then here is what I recommend:

1) Install the QT MPEG-2 Player Component if you have not already done so using one of the methods mectioned above.

2) Use the free MPEG Streamclip app to convert/demux your VOB titles to either a muxed MPEG (MPEG-2/MP2) file or to paired M2V and AIFF elementary stream files. (I prefer M2V/AIFF elementary streams because they aviods the file size limitations of the MPEG file container.)

3) Open the MPEG or M2V file in the QT 7 Pro Player app and open the "Properties" window.

4) Select/highlight the main file container track ("N/A" Track) and select the "Presentation" Tab.

5) Activate the following "Presentation" settings: "Automatically play movie when opened", "Enter fullscreen mode when opened", and "Automatically quit after playing".

6) Save the file as a "Reference" file using the "Save as..." File menu option

7) Set the reference file to open in the QT 7 Pro Player if not already defaulted for this option.

At this point double-clicking the reference file will open the MPEG or M2V/AIFF file(s) and begin playback in the "Full Screen" mode without opening the "Disappearing" controller and automatically close the player/quit the QT 7 Pro Player app when the movie finishes playback. In addition, the "Space" bar can be used to pause/play the movie without activating the "Disappearing" controller.

However, your use of the term "theater environment" makes me wonder if you have left out another important fact—i.e., that your goal may actually be to use your Mac Mini as a media playback server for a home entertainment system. If so, then this is a totally different matter having two possible approaches depending on the OS under which you plan to operate the system and how willing you are to convert the source media files.

a) Lion OS: Under Lion the best approach would be to use iTunes to serve M4V (H.264/AAC/AC3) file content to your audio and video equipment via the TV device. Its advantanges are that you can manage a large media library remotely via the TV device, locally via the sourcing device, or locally via mirroring from certain devices and retain AC3 DD5.1 playback options. The main disadvantage is that DVD media content must be converted for playback which can take large amounts of time.

b) Snow Leopard: Under Snow Leopard you have the same TV playback options with the same advantages and disadvantages. In addition, you can use the built-in Front Row app. The advantage here is that you can access and play your VIDEO_TS, iTunes, iMovie, iPhoto, etc. content using an TV-like menu without having to convert the original DVD data. The disadvantage is that the VIDEO_TS content must be moved to the start-up drive "Movies" folder and that AC3 DD5.1 "Passthrough" may not be supported. (I.e., have tested playback locally but do not have cables to connect my older MacBook Pro directly to my entertainment system.)