gst-convert: 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/gst-convert - from package: gnu-smalltalk

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

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