yuv4mpeg: 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/yuv4mpeg - from package: mjpegtools

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

Error in other languages:
yuv4mpeg: bevel nie gevind nie
yuv4mpeg: comandă negăsită
yuv4mpeg: comando não encontrado
yuv4mpeg: commande introuvable
yuv4mpeg: command not found
yuv4mpeg: käsku ei ole
yuv4mpeg: không tìm thấy lệnh
yuv4mpeg: komanda nerasta
yuv4mpeg: Kommando nicht gefunden.
yuv4mpeg: kommandot finns inte
yuv4mpeg: komut yok
yuv4mpeg: nie znaleziono polecenia
yuv4mpeg: níor aimsíodh an t-ordú
yuv4mpeg: no se encontró la orden
yuv4mpeg: no s'ha trobat l'ordre
yuv4mpeg: opdracht niet gevonden
yuv4mpeg: parancs nem található
yuv4mpeg: perintah tidak ditemukan
yuv4mpeg: príkaz nenájdený
yuv4mpeg: příkaz nenalezen
yuv4mpeg: команда не найдена
yuv4mpeg: командата не е открита
yuv4mpeg: 命令找不到
yuv4mpeg: コマンドが見つかりません