Default value is 1.
@item txt_duration
Sets the display duration of the decoded teletext pages or subtitles in
-milliseconds. Default value is 30000 which is 30 seconds.
+milliseconds. Default value is -1 which means infinity or until the next
+subtitle event comes.
@item txt_transparent
Force transparent background of the generated teletext bitmaps. Default value
is 0 which means an opaque background.