Mi rispondo da solo ma credo che a qualcun'altro possa interessare.
Credo di avere trovato il bandolo della matassa e il sw "giusto" (freeware) per risolvere il problema.
Il sw è
http://www.softpedia.com/get/Multimedia ... ager.shtml
Qui c'e' una piccola guida che mostra, come esempio, come far usare prioritariamente il codec XVID:
http://thehtpcrecord.com/index.php?opti ... d=99999999
La spiegazione la si trova nell'help di RadLight:
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Each filter is registered with a merit value. When the
filter graph manager builds a graph, it enumerates all the
filters registered with the correct media type. Then it
tries them in order of merit, from highest to lowest. (It
uses additional criteria to choose between filters with
equal merit.) It never tries filters with a merit value less
than or equal to MERIT_DO_NOT_USE. A filter that
should never be considered for ordinary playback should
have a merit of MERIT_DO_NOT_USE or less. Filters can
be registered with intermediate values not defined by
this enumeration, such as MERIT_NORMAL + 1.
STANDARDIZED MERIT VALUES
MERIT_PREFERRED = 0x800000
MERIT_NORMAL = 0x600000
MERIT_UNLIKELY = 0x400000
MERIT_DO_NOT_USE = 0x200000
MERIT_SW_COMPRESSOR = 0x100000
MERIT_HW_COMPRESSOR = 0x100050
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