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Afficher le format du stream audio :
$ ffmpeg -i <nom de la video> 2>&1 \; | grep Audio | awk '{print $4}'

Convertir si besoin en mp4 :
$ ffmpeg -i video.m4v video.mp4

Réduire la résolution des vidéos :
Soit une vidéo 1920×1440 qui pèse 118Mo
$ ffmpeg -i input.MP4 -vf scale=480:360 output.MP4
—> Une vidéo 480×360 qui pèse 3Mo

Convertir une vidéo .MP4 au format .webm :
$ ffmpeg -i input.MP4 -c:v libvpx -b:v 1M -c:a libvorbis output.webm

La même chose en 1 passe :
(Convertir une grosse vidéo .MP4 en une petite .webm)
$ ffmpeg -i input.MP4 -vf scale=480:360 -c:v libvpx -b:v 1M -c:a libvorbis output.webm

Concaténer des vidéos :
Créer un fichier avec la liste des videos à concaténer :
$ find . -name "*.mp4" -exec echo file \'{}\' >> list.txt \;

Concaténer les vidéos :
$ ffmpeg -f concat -i list.txt -c copy final.mp4

Installation pour MacOs :
$ brew install ffmpeg --with-libvpx --with-libvorbis --with-fdk-aacc

Method 1: PIPED while-read loop

#!/bin/bash
FILENAME=$1
count=0
cat $FILENAME | while read LINE
do
       let count++
       echo "$count $LINE"
done

echo -e "\nTotal $count Lines read"

Method 2: Redirected “while-read” loop

#!/bin/bash
FILENAME=$1
count=0

while read LINE
do
      let count++
      echo "$count $LINE"

done < $FILENAME

echo -e "\nTotal $count Lines read"

Method 3:while read LINE Using File Descriptors

#!/bin/bash
FILENAME=$1
count0=
exec 3<&0
exec 0< $FILENAME

while read LINE
do
        let count++
        echo "$count $LINE"
done

exec 0<&3
echo -e "\nTotal $count Lines read"

Method 4: Process file line by line using awk

#!/bin/bash
FILENAME=$1

awk '{kount++;print  kount, $0}
     END{print "\nTotal " kount " lines read"}' $FILENAME

Time Comparison

# du -h bigfile.txt
70M     bigfile.txt
# wc -l bigfile.txt
900000 bigfile.txt

# time ./method1.sh bigfile.txt >/dev/null
real    6m2.911s
user    2m58.207s
sys     2m58.811s

# time ./method2.sh bigfile.txt > /dev/null
real    2m48.394s
user    2m39.714s
sys     0m8.089s

# time ./method3.sh bigfile.txt > /dev/null
real    2m48.218s
user    2m39.322s
sys     0m8.161s

# time ./method4.sh bigfile.txt > /dev/null
real    0m2.054s
user    0m1.924s
sys     0m0.120s

Source de cet article : http://www.bashguru.com/2010/05/how-to-read-file-line-by-line-in-shell.html
(Article complet avec explications, mais aussi plein de pubs^^)

Brackets
if [ CONDITION ]           Test construct
if [[ CONDITION ]]         Extended test construct
Array[1]=element1        Array initialization
[a-z]                               Range of characters within a Regular Expression

Curly Brackets
${variable}                                                          Parameter substitution
${!variable}                                                         Indirect variable reference
{ command1; command2; . . . commandN; }    Block of code
{string1,string2,string3,…}                                 Brace expansion
{a..z}                                                                   Extended brace expansion
{}                                                                        Text replacement, after find and xargs

Parentheses
( command1; command2 )                       Command group executed within a subshell
Array=(element1 element2 element3)      Array initialization
result=$(COMMAND)                               Command substitution, new style
>(COMMAND)                                          Process substitution
<(COMMAND)                                          Process substitution

Double Parentheses
(( var = 78 ))                            Integer arithmetic
var=$(( 20 + 5 ))                      Integer arithmetic, with variable assignment
(( var++ ))                                C-style variable increment
(( var– ))                                  C-style variable decrement
(( var0 = var1<98?9:21 ))       C-style trinary operation