DV playback issue

[bsw11]

I have a lot of DV video files loaded in from tape on a mac.
The ones that are recorded with 32bit audio play just fine and use the dvsd codec.
The ones that are recorded with 48bit audio play slow 18 fps - they use the dvc codec.

Is there a way to force use of the dvsd codec or some other fix for this?

[VLC_help]

--codec=<string> Preferred decoders list
List of codecs that VLC will use in priority. For instance,
'dummy,a52' will try the dummy and a52 codecs before trying the other
ones. Only advanced users should alter this option as it can break
playback of all your streams.

http://wiki.videolan.org/VLC_command-line_help