Some users may have aware that the encoded audio using x26XGUIEx are 2-channels only when using AAC.
To read video with 5.1ch AC-3 or AAC, L-Smash importer usually works(it works on mine). If not, the DirectShow import filter should work. However, the encoded video will contains 2 audio channels only.
Note: If your source is 5.1ch AC-3, reading through L-SMASH and you choose the FFMPEG AC-3 encoder option, the encoded video will retain 5.1ch.
In order to import and cut a 5.1ch(AAC) video and encode it back to a 5.1ch(AAC) video, here is one way (supposed to be a lossless operation):
>Get the necessary files HERE
>Put the files into their corresponding folders in your local AviUtl installation
> Demux your source file. Only the audio stream is needed.
> Get AudioCoder, and set the encoding option like the following:
(the use of FAAC MPEG2 format is IMPORTANT, tweak other things as needed)
> Open AviUtl and set Import Plugin Priority. Put the FAW entry above L-SMASH
> Load your video, then replace the audio data with: [File>Import Audio], then choose your aac file.
> A Note of Health Warning: DO NOT Playback this audio! It is just noise and can damage your hearing or equipment.
>Perform the usual cutting or filtering. When ready to encode…
>In the x26XGUIEx, set the audio part like the following:
Choose FAW, and point to the recently downloaded fawcl.exe
>If everything goes fine, the GUI’s log window looks like the following:
> Before playback. Check the audio format is correct (The output format is ALWAYS AAC, the same as your source AAC file):
The above information was gathered piece-by-piece from many old pages and then tested myself.
So until someone decided to write a sophisticated channel mixer and encoder for AviUtl, you’ll better to stick with stereo audio, use AC-3 all the way… or use other AV editor.