#!/bin/bash
# Thomas Lewiner, http://www.carva.org/thomas.lewiner
# Matmidia Lab, Dept of Mathematics, PUC-Rio de Janeiro
# September 16th, 2009
#
# video thumbnail generator
# using bash, ffmpeg and ImageMagick
#
# usage:
# ./videothumb.bash file.avi
#
# edit the settings in this file following the comments
# works with any video file readable by ffmpeg
#

# width of a single frame (without shading margins)
width=128 ;

# shadow size
shadow=5 ;

# rounded corner size
round=6 ;

# frame shift: uncomment here and comment the marked line for a fixed shift between pages
# shift=50;

# automatic page shift to fit the thumbnail in a given width
total_width=450;

# second skip: get a frame every $sec_skip seconds
sec_skip=19;


for vid in "$1" ;
do
# extract the total time of the video in seconds
    let "total_time=$(ffmpeg -i ${vid} 2>&1 | grep "Duration" | cut -d ' ' -f 4 | sed -e 's/\([0-9]*\):\([0-9]*\):\([0-9]*\).*/\1 * 3600 + \2 * 60 + \3/')" ;

# extract rounded frames from vid (starting from the second frame of the sequence, set time to 0 for the first frame)
    count=0;
    time=$sec_skip;
    while [ $time -lt $total_time ] ;
    do
        ffmpeg -y -i ${vid} -vcodec png -f rawvideo -vframes 1 -an -ss ${time} thumb.png 2> /dev/null ;        
        convert -resize $width -matte -virtual-pixel transparent -channel A -blur 0x$round  -threshold 50% +channel thumb.png thumbs-$(printf '%03d' ${count}).png ;
        let "time += $sec_skip" ;
        let "count += 1";
    done ;
    rm thumb.png ;

# add shadows
    for p in thumbs-*.png ;
    do
        convert -page +${shadow}+${shadow} $p -matte \( +clone -background black -shadow 60x${shadow}+${shadow}+${shadow} \) +swap -background none -mosaic ${p/.png/_shadow.png} && rm $p ;
    done ;

# frame shift: comment the next line for a fixed shift between frames
    let "count=$count/2";
    let "shift=($total_width - $width - $shadow)/($count - 1)";
    echo "$vid lasts $total_time seconds, leading to 2x$count retained frames (each $sec_skip seconds), set to $width px extent each, rounded by $round px, shadowed of $shadow px and shifted by $shift px";

# compose the final images
    offset=0 ;
    cmd="" ;
    for ((c=0; c<${count}; c+=1)) 
    do
        cmd="-page +${offset}+0 thumbs-$(printf '%03d' ${c})_shadow.png $cmd" ;
        let "offset += $shift" ;  
    done ;
    convert  $cmd  -background transparent -layers mosaic  "${vid/[.]*/_thumb1.png}";

    offset=0 ;
    cmd="" ;
    for ((c=${count}; c<=2*${count}; c+=1)) 
    do
        cmd="-page +${offset}+0 thumbs-$(printf '%03d' ${c})_shadow.png $cmd" ;
        let "offset += $shift" ;  
    done ;
    convert  $cmd  -background transparent -layers mosaic  "${vid/[.]*/_thumb2.png}";
    
    rm thumbs-*_shadow.png ;
done ;