Support for text roles

[SebastienChauvin]

Suggestion from Kaltura: kaltura#1049 (comment)

Add a new “role” enum to support:

• normal subtitle
• describe video subtitles
• forced subtitles
• closed captioning

DASH

https://dashif.org/docs/IOP-Guidelines/DASH-IF-IOP-Part9-v5.0.0.pdf

Dash-Industry-Forum/DASH-IF-IOP#165

In ISO/IEC 23009-1:2022(E) ( https://standards.iso.org/ittf/PubliclyAvailableStandards/c083314_ISO_IEC 23009-1_2022(en).zip )

We have : 5.8.5.5 ****DASH role scheme
saying that role can be description / forced-subtitle

[SebastienChauvin]

https://srgssr-ch.atlassian.net/wiki/spaces/AWS/pages/960594199/Providing+accessibility+with+Stream+Packaging

[SebastienChauvin]

Text track

role=subtitle (default) ->
HLS subtitle without flag
DASH no role, no accessibility

role=caption ->
HLS closed-caption without flag
DASH <Accessibility schemeIdUri="urn:mpeg:dash:role:2011" value="caption"/>

role=description ->
HLS #EXT-X-MEDIA:TYPE=SUBTITLES,CHARACTERISTICS="public.accessibility.transcribes-spoken-dialog,public.accessibility.describes-music-and-sound"
DASH <Accessibility schemeIdUri="urn:mpeg:dash:role:2011" value="caption"/>

role=forced-subtitle ->
HLS FORCED
DASH <Role schemeIdUri="urn:mpeg:dash:role:2011" value="forced-subtitle"/>

Audio track

role=description ->
HLS #EXT-X-MEDIA:TYPE=AUDIO,CHARACTERISTICS="public.accessibility.describes-video"
DASH