mpegdemux: 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/mpegdemux - from package: mpegdemux

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

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