consumer_avformat.c: add support for an=1, vn=1, acodec=none, and vcodec=none options...

[melted] / demo / mlt_attributes

inigo clip1.dv \
meta.attr.location=1 meta.attr.location.markup="Location" \
meta.attr.exclusive=1 meta.attr.exclusive.markup="Exclusive" \
meta.attr.special=1 meta.attr.special.markup="Special" \
meta.attr.super=1 meta.attr.super.0="Line 1" meta.attr.super.1="Line 2" \
-filter data_show \
$*