Print to File list of media file names, types and most importantly length
You may install the command line utility exiftool.

Then open a text file and copy/paste the following bash script:

#!/bin/sh

find "~/Movies/" -name "*" -not -name ".*" -type f | while read file
do
    FILETYPE=$(exiftool  -p "\$FileType" "${file}")
    FPS=$(exiftool  -p "\$FrameRate" "${file}")
    TOTALFRAMES=$(exiftool  -p "\$FrameCount" "${file}")
    DURATION=$[TOTALFRAMES*FPS]
    echo ${file} ${FILETYPE} ${DURATION} &gt; output.txt
done


Replace ~/Movies/ with the full path containing the movie files and output.txt with your resulting file name.

Save the file to your user's home folder, as 'meta_generator' or by whatever name you want.

Then fire up /Utilities/Terminal.app and type:

chmod +x meta_generator
./meta_generator


Edit:
I just saw that you wanted the length in seconds, so I've replaced the Duration tag.

By multiplying the framerate and the total frame count, you'll get the desired seconds..

But you may find other easier ways though :)