All-In-One Downmixer-Converter For .aac?

[LouieChuckyMerry]

Hello, and thanks in advance for any viable advice; you're helping prevent hair loss. Long story short, I've several hundred video files of varying type that contain audio of varying type where I want to demux the audio, downmix-convert it to 128 kbps, 2-channel .aac (though I'm very open to suggestions for a better setting), then remux because I've no use for multichannel, high bitrate audio and would be happy for the extra space. After several weeks of diligent effort I've learned how to demux and remux reasonably confidently, and to downmix-convert .ac3 and .mp3 pretty consistently, but when it comes to downmixing-converting .aac audio I'm having some issues. I've tried xrecode ii, foobar2000, MeGUI, AVANTI, BeSweet, EAC3To, and a couple more I can't remember. All of them downmix-convert some .aac files, none of them downmix-convert all .aac files, and I've some .aac files that none of them will downmix-convert. Sometimes I'll take two .aac files that MediaInfo says are the same and be able to downmix-convert one but not the other (although given that MediaInfo sometimes states, for example, that the audio file in an .mp4 is 6-channel but that it's 2-channel after demuxing I'm not sure how much stock I put in MediaInfo). I've spent countless hours Googling and experimenting but to no avail. Please, is there any freeware app, or combination of apps, that can handle all of the seeming myriad different .aac types? I'd prefer a portable app, but begger's can't be choosers. Thank you again for your time.


15 January 2010:

After checking several of the "Similar Threads" below I've found the free version of NCH Software's Switch Audio Converter to be stellar, despite the need to install it, as it's very easy to use and has downmixed-converted (so far) every .aac file I've thrown it's way. Also, foobar2000 works well and is portable, but it's only accepted about 75% of the .aac files I've tried to downmix-convert with it. I'll next check out dbPowerAmp. Before opening this thread I searched the audio forum here for answers but came up with nothing; however, the "Similar Threads" are just what I was looking for when I searched, so no complaints. I apologize if I wasted anybody's time, as that was not my intent, and I thank the forces that be for the "Similar Threads."