subtitle streams are sometimes not detected in vob

[behrisch]

subtitle streams can be late to the party, see https://trac.ffmpeg.org/ticket/598. A possible fix is to have a (configurable?) larger probe interval when detecting the streams as mentioned here: https://trac.ffmpeg.org/ticket/598#comment:19. In my example ffmpeg -probesize 100M -analyzeduration 100M -i S01E01.vob detected all streams (80M was not enough).