Support mp3 encoding step in bit rate test.

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

src/ber-test.sh

 # pseudo random pattern
 
 PATTERN=4e1243bd22c66e76c2ba9eddc1f91394e57f9f83
+TRANSFORM=$1
 
 for i in test/T*
 do
   echo $i
   audiowmark add $i t.wav $PATTERN >/dev/null
+  if [ "x$TRANSFORM" == "xmp3" ]; then
+    if [ "x$2" == "x" ]; then
+      echo "need mp3 bitrate" >&2
+      exit 1
+    fi
+    lame -b $2 t.wav t.mp3 --quiet
+    rm t.wav
+    ffmpeg -i t.mp3 t.wav -v quiet
+
+    # some (low) mpeg quality settings use a lower sample rate
+    if [ "x$(soxi -r t.wav)" != "x44100" ]; then
+      sox t.wav tr.wav rate 44100
+      mv tr.wav t.wav
+    fi
+  elif [ "x$TRANSFORM" == "x" ]; then
+    :
+  else
+    echo "unknown transform $TRANSFORM" >&2
+    exit 1
+  fi
   audiowmark cmp $i t.wav $PATTERN
 done | grep bit_error_rate | awk '{ er += $2; n++; if ($2 > max_er) max_er = $2;} END { print er / n, max_er; }'