position
Defines when the ad break should be played. Default is 'pre'.
Allowed values are:
'pre': pre-roll ad
'post': post-roll ad
fractional seconds: '10', '12.5' (mid-roll ad)
percentage of the entire video duration: '25%', '50%' (mid-roll ad)
timecode hh:mm:ss.mmm: '00:10:30.000', '01:00:00.000' (mid-roll ad)