awk -F' - |:[0-9]+/' '
FILENAME=="f1" {
   if (/^#EXTINF/) chn=$NF
   if (/^http:/) chg2id[chn] = $NF
   next
}

{ lines[FNR] = $0 }

/^#SERVICE/ { servline = FNR; next }

/^#DESCRIPTION/ {
   chn = substr($0,14)
   gsub(/^ +| +$/, "", chn)
   if (chn)  {
      sub( /^#SERVICE 1:(0:)+/, "#SERVICE " chg2id[chn], lines[servline])
   }
   next
}

END {
   for (i=1;i<=FNR;++i)
      print lines[i]
}' f1 f2