a52dec: command not found

Have You tried accessing the binary with the full path?

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/a52dec - from package: liba52-0.7.4-dev

You may install the required package with command apt-get install {package}
Error in other languages:
a52dec: bevel nie gevind nie
a52dec: comandă negăsită
a52dec: comando não encontrado
a52dec: commande introuvable
a52dec: command not found
a52dec: käsku ei ole
a52dec: không tìm thấy lệnh
a52dec: komanda nerasta
a52dec: Kommando nicht gefunden.
a52dec: kommandot finns inte
a52dec: komut yok
a52dec: nie znaleziono polecenia
a52dec: níor aimsíodh an t-ordú
a52dec: no se encontró la orden
a52dec: no s'ha trobat l'ordre
a52dec: opdracht niet gevonden
a52dec: parancs nem található
a52dec: perintah tidak ditemukan
a52dec: príkaz nenájdený
a52dec: příkaz nenalezen
a52dec: команда не найдена
a52dec: командата не е открита
a52dec: 命令找不到
a52dec: コマンドが見つかりません