There is MPEG Streamcllp which can export with or without video into QuickTime .mov files. A quick test of converting a video file without video suggests the default is to convert to PCM at whatever frequency (Hz) the original was (example was 16-Bit 48 KHz.) However if you are wanting to construct a video such as a slideshow, this program will not do it. It also does not support mp3 input but should support aac mp4 audio as that's one of its export options (as well as WAV/AIFF.) This was tested on both MacOS and Win 7. If you do test this, make sure the files play OK.
MPEG Streamcllp requires QuickTime 7 to be installed. I was unable to get the Win version of QT via Win 7 but was able to get it via MacOSX. So I have a copy of the Win QT7 installer if you are unable to get it.

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