System info

Operating System: Debian GNU/Linux 11 (bullseye)
Shaka Packager Version: shaka-packager version v2.6.1-634af65-release

Issue and steps to reproduce the problem

I'm running into an issue setting the roles stream descriptor option for content containing descriptive audio tracks. The DASH spec specifically defines these as:

description - Textual or audio media component containing a textual description (intended for
audio synthesis) or an audio description describing a visual component.

From the shaka-packager docs, it appears it only supports a subset of the values outlined in the DASH specification:

Optional semicolon separated list of values for DASH Role element. The value should be one of: caption, subtitle, main, alternate, supplementary, commentary and dub. See DASH (ISO/IEC 23009-1) specification for details.

However, checking the DASH (ISO/IEC 23009-1) specification, section 5.8.5.5 DASH role scheme (Table 29), defines many more values for the roles:

• caption
• subtitle
• main
• alternate
• supplementary
• commentary
• dub
• description
• sign
• metadata
• enhanced-audio-intelligibility
• emergency

Packager Command:

shaka-packager \
in=./input.mp4,stream=video,init_segment=./video/video_init.mp4,segment_template=./video/video_$Number$.m4s \
in=./input.mp4,stream=audio,language=en,roles=main,init_segment=./audio/audio_main_init.mp4,segment_template=./audio/audio_main_$Number$.m4s \
in=./descriptive-audio.mp4,stream=audio,language=en,roles=description,init_segment=./audio/audio_desc_init.mp4,segment_template=./audio/audio_desc_$Number$.m4s \
--fragment_duration 6 --segment_duration 6 --generate_static_live_mpd --mpd_output ./manifest.mpd

Extra steps to reproduce the problem?
(1) include roles=description in DASH stream descriptor options

What is the expected result?
Generates a DASH manifest with a description role

What happens instead?
Shaka throws an error:

[1127/214613:ERROR:period.cc(208)] Unrecognized role 'description'