I have found a way to encode video in AviUtl directly to MP4-DASH. The method needs a little modification to an INI file in the ./Plugin sub-folder.
Details here:

http://mavericktse.mooo.com/wordpress/archives/2204

the key command line options are:

Code:
--fragment 1 --dash 0
which will be passed to remuxer.exe (part of L-SMASH)

using MediaInfo, I confirmed that the encoded file is indeed identified as DASH, but I'd like to confirm:
1) are there any fail-case using this method?
2) is it DASH in the appropriate form?
3) is DASH video get processed faster when uploading to Youtube?