mp4extract: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/mp4extract - from package: libmp4v2

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/mp4extract - from package: mp4v2-utils

You may install the required package with command apt-get install {package}

Error in other languages:
mp4extract: bevel nie gevind nie
mp4extract: comandă negăsită
mp4extract: comando não encontrado
mp4extract: commande introuvable
mp4extract: command not found
mp4extract: käsku ei ole
mp4extract: không tìm thấy lệnh
mp4extract: komanda nerasta
mp4extract: Kommando nicht gefunden.
mp4extract: kommandot finns inte
mp4extract: komut yok
mp4extract: nie znaleziono polecenia
mp4extract: níor aimsíodh an t-ordú
mp4extract: no se encontró la orden
mp4extract: no s'ha trobat l'ordre
mp4extract: opdracht niet gevonden
mp4extract: parancs nem található
mp4extract: perintah tidak ditemukan
mp4extract: príkaz nenájdený
mp4extract: příkaz nenalezen
mp4extract: команда не найдена
mp4extract: командата не е открита
mp4extract: 命令找不到
mp4extract: コマンドが見つかりません