Unbuffered parsing of mplayer output in shell script

Question

After trying several variants with stdbuf and unbuffer for parsing mplayer (and in my case also libdvdnav) output in a shell script, I didn't found a working solution. Here is my shell script without the part that parses the output - it just runs echo over each line.

#!/bin/bash
IN=video.iso
OUT=video.mpg

IFS=$'\n'
for line in `stdbuf -oL -eL mplayer -msglevel identify=6 -dumpstream -dumpfile $OUT dvdnav://1/$IN 2>&1`; do
    echo "mplayer: $line"
done

The output is buffered even when using stdbuf, so I'm not able to parse each line in real time. Is there a way to catch mplayer output when using the dvdnav target?