Ok example file is at:

http://zaheer.merali.org/random/test.m4a

OK, we need (in qtdemux)

- fourcc: alac, mediatype: audio/x-alac, with properties:
- sample_size (stsd+10)
- codec_data (stsd+20, where the first 4 bytes are the length (always 36) and
the second 4 bytes are 'alac')
- channels/rate (already there)

With those, ffmpeg will decode it correctly. I'm stumped once more by qtdemux,
but will try to add it.

Added.