$imagenes = Get-ChildItem *.jpg
 
foreach ($img in $imagenes) {
 
    $salida = "TXT_$($img.Name)"
 
    ffmpeg -y `
        -i "$($img.FullName)" `
        -vf "drawtext=fontfile='C\:/Windows/Fonts/arial.ttf':text='by morkey':x=20:y=800:fontsize=50:fontcolor=red" `
        "$salida"
}