6ch aac to 2ch aac without reencode?

[DerWish]

I have an odd problem.

I encoded very much files and now i noticed that the audio is faulty.

Instead of 2ch the audio is flaged as 6ch. But there are no no data/sound in the other channels than left and right. Thats annoying when i play these files on atv 4 with forced dolby settings. The atv plays it as stereo left and right. Before i forced dolby in the settings my reciever was able to make dolby prologic II out of these files. But i want dolby because much of the files also have ac3 6ch, so i have to set somehow these files to stereo aac in the file instead of 6ch.

How can i change it to be flagged correct to 2 ch without re-encoding?

Don´t want to encode all the files again. Weeks of work will be wasted!
Googled much but doesn´t find anything.

Can use mac and windows.

I hope there is a way to do that. Best with batch if possible.

Thx in advance
DerWish

[Baldrick]

I haven't seen any method to do it without reconverting.

[hello_hello]

Are there only two channels flagged as six or are there two channels plus four channels containing silence? If it's the latter there's probably not much you can do and I'm not sure how 2ch AAC would end up incorrectly flagged as 6ch.

[KarMa]

OP says that these AC3 files contain a mixture of 2ch and 6ch audio, so it just gets completely encoded as 6ch AAC. The AC3 files need to be cut into stereo only and surround only files. Delaycut can make easier work of losslessly cutting AC3 files.

On some HDTV channels, they will jump between Stereo and Surround. The switch will happen slightly before or right at the start of a program, requiring the first few frames of audio to be cut if you are to get all Stereo or all Surround audio. It's much worse to have a few moments of Surround in a mostly Stereo program, than the other way around imo. As the entire program will be encoded in Surround with many empty channels.

[hello_hello]

My interpretation... he's got a bunch of AAC files that should be 2ch and he's also got files that contain AC3 5.1ch. Maybe I'm wrong but there's a Dolby setting involved that sounds like it might get the player to downmix to Prologic but the AAC is throwing a spanner in the works, or given the plethora of video containing both stereo AAC and 5.1ch AC3 to make them Apple friendly, forcing dolby could even be a "bypass the stereo AAC" type setting. I vaguely remember something like that for older devices that could only do AC3 pass-through.

If you have enough familiarity with Apple products to know what an atv 4 is without having to google it and take a guess, you'd probably have a good chance of understanding the problem, but I had to google and guess so I could be getting it all wrong.