State of FORCED tag in HLS

Question

Created Aug ’22

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I cannot seem to get the FORCED tag available in the HLS standard to work correctly. Using the native HLS players in safari, iOS, and tvOS, none of them render a subtitle track defined as

#EXT-X-MEDIA:TYPE=SUBTITLES,URI="text/text-open.m3u8",GROUP-ID="text",LANGUAGE="sv",NAME="Svenska",DEFAULT=YES,AUTOSELECT=YES,FORCED=YES

or

#EXT-X-MEDIA:TYPE=SUBTITLES,URI="text/text-open.m3u8",GROUP-ID="text",LANGUAGE="sv",NAME="Svenska",DEFAULT=NO,AUTOSELECT=YES,FORCED=YES

I've seen that Apple TV+ uses forced subtitles with the same settings as the latter example in their playlists, and I assume they work there. Is there something obvious that I'm missing?

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Answer 1

Media Engineer OP

Apple

Aug ’22

There is nothing obviously wrong with either version, but it is impossible to check these in isolation.

If you try with DEFAULT=YES,AUTOSELECT=YES,FORCED=NO do the subtitles get selected? With those settings can you select them by hand?

If you run mediastreamvalidator does it complain about any subtitle issues?

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Answer 2

Fredrik_Lundkvist OP

Aug ’22

Some more info: When I set DEFAULT=YES,AUTOSELECT=YES,FORCED=NO for the subtitle track, they get auto selected, and are selectable by hand in all the players I've tested.

Running mediastreamvalidator on a manifest with the above settings works fine.

Then I tried setting the following:

#EXT-X-MEDIA:TYPE=SUBTITLES,URI="text/text-open.m3u8",GROUP-ID="text",LANGUAGE="sv",NAME="Svenska OPEN",DEFAULT=YES,FORCED=YES
#EXT-X-MEDIA:TYPE=AUDIO,URI="cmaf-audio-en-aac-2ch-192/cmaf-audio-en-aac-2ch-192.m3u8",GROUP-ID="AAC-0",LANGUAGE="en",ASSOC-LANGUAGE="sv",NAME="Engelska",DEFAULT=YES,AUTOSELECT=YES,CHANNELS="2"

The subtitles are not selectable in the UI, and do not render. The only subtitle-related info from mediastreamvalidator is:

text/text-open.m3u8

--------------------------------------------------------------------------------

HTTP Content-Type: application/x-mpegurl



Processed 1 out of 1 segments

Average segment duration: 2816.080000

Total segment bitrates (all discontinuities): average: 0.13 kb/s, max: 0.13 kb/s

Rendition group ID: text





Discontinuity: sequence: 0, parsed segment count: 1 of 1, duration: 2816.080 sec

Track ID: 200

Which I interpret as no errors being detected.

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