How to set subtitles as forced subtitles via Mediaconvert

Hi,

we are creating HLS- and DASH-Outputs via MediaConvert. Our source assets provide multiple subtitles(captions) in the ttml-format. Some of these subtitles are forced subtitles and we need to flag those properly in the respective playlists created for HLS/DASH (mpd/m3u8). We set the destination type of the subtitles in the output settings to WebVTT.

Given a main-m3u8 file created by MediaConvert the following lines are refering to the added subtitles:

#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="subs_hu",DEFAULT=YES,AUTOSELECT=YES,FORCED=NO,LANGUAGE="hun",URI="hlssubtitles_hu.m3u8" #EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="subs_en_US",DEFAULT=NO,AUTOSELECT=YES,FORCED=NO,LANGUAGE="eng",URI="hlssubtitles_en_US.m3u8" #EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="forced_subs_hu",DEFAULT=NO,AUTOSELECT=YES,FORCED=NO,LANGUAGE="hun",URI="hlsforced_subtitles_hu.m3u8"

For each entry there is a value "FORCED=NO". How can we alter this value for forced subtitles to "FORCED=YES"?

Similarly how do we set this up for DASH-Playlists? Subtitles were added in the following form:

<AdaptationSet mimeType="text/vtt" lang="hu"> <Role schemeIdUri="urn:mpeg:dash:role" value="subtitle"/> <Label>forced_subs_hu</Label> <Representation id="11" bandwidth="256"> <BaseURL>dashforced_subtitles_hu.mpd</BaseURL> </Representation> </AdaptationSet>

According to DASH's ISO/IEC 23009-1:2019

we should be able to set the role-value to forced-subtitles.