I found out, that mythweb does not allow me to download the imported mythnettv files. This is due to the fact, that they have no file sufix (.avi etc). To make it work, just edit

/var/www/mythweb/modules/stream/stream_raw.pl

to include the following code in the section “# File type”

elsif ($&;basename =~ /tmp/) {
$&;type   = 'video/avivideo';
$&;suffix = '.avi';
}

I am pretty sure not all files are realy “avi”, but for all intendet purposes (downloading, playing) its fine with me.