YUV420Down2x2: 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

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/YUV420Down2x2 - from package: dirac

You may install the required package with command apt-get install {package}
Error in other languages:
YUV420Down2x2: bevel nie gevind nie
YUV420Down2x2: comandă negăsită
YUV420Down2x2: comando não encontrado
YUV420Down2x2: commande introuvable
YUV420Down2x2: command not found
YUV420Down2x2: käsku ei ole
YUV420Down2x2: không tìm thấy lệnh
YUV420Down2x2: komanda nerasta
YUV420Down2x2: Kommando nicht gefunden.
YUV420Down2x2: kommandot finns inte
YUV420Down2x2: komut yok
YUV420Down2x2: nie znaleziono polecenia
YUV420Down2x2: níor aimsíodh an t-ordú
YUV420Down2x2: no se encontró la orden
YUV420Down2x2: no s'ha trobat l'ordre
YUV420Down2x2: opdracht niet gevonden
YUV420Down2x2: parancs nem található
YUV420Down2x2: perintah tidak ditemukan
YUV420Down2x2: príkaz nenájdený
YUV420Down2x2: příkaz nenalezen
YUV420Down2x2: команда не найдена
YUV420Down2x2: командата не е открита
YUV420Down2x2: 命令找不到
YUV420Down2x2: コマンドが見つかりません