mp4h: 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 Debian possible default full paths are:

/usr/bin/mp4h - from package: mp4h

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

Error in other languages:
mp4h: bevel nie gevind nie
mp4h: comandă negăsită
mp4h: comando não encontrado
mp4h: commande introuvable
mp4h: command not found
mp4h: käsku ei ole
mp4h: không tìm thấy lệnh
mp4h: komanda nerasta
mp4h: Kommando nicht gefunden.
mp4h: kommandot finns inte
mp4h: komut yok
mp4h: nie znaleziono polecenia
mp4h: níor aimsíodh an t-ordú
mp4h: no se encontró la orden
mp4h: no s'ha trobat l'ordre
mp4h: opdracht niet gevonden
mp4h: parancs nem található
mp4h: perintah tidak ditemukan
mp4h: príkaz nenájdený
mp4h: příkaz nenalezen
mp4h: команда не найдена
mp4h: командата не е открита
mp4h: 命令找不到
mp4h: コマンドが見つかりません