tsdecrypt_ffdecsa: 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/tsdecrypt_ffdecsa - from package: tsdecrypt

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