Index: idvid
===================================================================
--- idvid   (revision 2061)
+++ idvid   (working copy)
@@ -88,6 +88,7 @@
 MATCH_FORMAT=""
 MATCH_TVSYS=""
 TABULAR=false
+USE_NAVLOG=false
 ID_FILES=""

 mkdir -p "$STAT_DIR"
@@ -295,12 +296,28 @@
     # If doing -fast identification, skip "accurate" length determination
     if $FAST; then
         :
-    else
-        # Determine duration by playing the video into /dev/null and doing
-        # tons of filtering. Time consuming, but presumably more accurate.
-        V_DURATION=$(LC_ALL=C mencoder -ovc frameno -oac pcm -noskiplimit \
+    else # make a nav_log: can be reused, especially by todisc for fast seeking
+        if  [[ -s "$INFILE".nav_log ]]; then
+            echo "Using ${INFILE}.nav_log"
+            echo "If you don't want to use this file please delete it"
+            USE_NAVLOG=:
+        elif  [[ ${INFILE##*.} =~ [MmPpGg] ]] && hash tcdemux 2>/dev/null; then
+        # use tcdemux if present, and  if *.mpg extension
+            NAVSEEK_CMD=(nice tcdemux  -f $ID_VIDEO_FPS -W -i "$INFILE")
+            "${NAVSEEK_CMD[@]}" >  "$INFILE".nav_log 2>&1
+            USE_NAVLOG=:
+        else
+            # Determine duration by playing the video into /dev/null and doing
+            # tons of filtering. Time consuming, but presumably more accurate.
+            V_DURATION=$(LC_ALL=C mencoder -ovc frameno -oac pcm -noskiplimit \
             "$INFILE" -o /dev/null 2>/dev/null | tr '\r' '\n' | grep ^Pos: | \
             tail -n 1 | sed s/^.*Pos:// | awk '{print $1}' | sed s/[.][0-9]s//)
+        fi
+        if $USE_NAVLOG; then
+            ID_VIDEO_FRAMES=$(awk '{ field = $2 }; END{ print field }'  < "${INFILE}".nav_log)
+            V_DUR=$(bc <<< "$ID_VIDEO_FRAMES / $ID_VIDEO_FPS")
+            V_DURATION=${V_DUR%%.*} # final value is integer ( seconds )
+        fi
     fi

     # Use mplayer-reported length as a last resort (truncate floating-point)