for corona streams, asfrecorder bombs out with
unknown content-type: application/vnd.ms.wms-hdr.asfv1
Patches 687466 and 956813 only fixed the error message;
the resulting file produced by asfrecorder turned out
to be unusable in the majority of cases. That's
because asfrecorder did by default only enable one
substream even if there were several. This patch fixes
the problem and additionally improves output.