請參考下述網頁介紹：
http://forum.doom9.org/showthread.php?p=666230

AAC -> AC3 Fast GraphEdit/ffdshow way:

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Fast method with ffdshow:

get GraphEdit from: http://www.3ivx.com/download/windows.html or download look for the link to GraphEdit in the upper right corner.

get new FFDSHOW from: http://www.aziendeassociate.it/cd.asp?dir=/ffdshow download newest version of ffdshow

-install ffdshow
-activate decoding for aac!
-extract graphedit in a folder
-start graphedit
-drag&drop AAC-file in GraphEdit window
-click and remove "default direct sound device"
- click Menu graph->insert new filter->DirectShowFilter->Filewriter and "insert filter", choose filename "convert.ac3"
-right click on ffdshow->properties->output->AC3 and "allow direct-to-file output" and "don't use Waveformatextensible"
-click ok

[see figure 1]
http://forum.doom9.org/attachment.p...49&d=1118316513

-connect ffdshow filter with the file writer "convert.ac3" filter
-click play to start conversion and wait until its finished

[see figure 2]
http://forum.doom9.org/attachment.p...51&d=1118316522

If your output stutters it is very likely that your sampling rate is 44KHz and not 48KHz Some soundcard don't output 44KHz over S/PDIF correctly. To solve this, activate the resampler in ffdshow and set it to "Resample if sampling rate below... 48000Hz".