Embedded Closed Captions on HLS stream to Android Client

[drchandler 0]

There have been numerous posts on embedded closed captions not appearing during HLS re-muxing to Android/AndroidTV clients when pulling from HDHomerun and other tuners. Note, these captions are embedded in the video stream and not sent as independent sidecar data (e.g. srt/webvtt). These embedded closed captions are present in the video files because once the OTA recording is complete they do appear on playback on Android/AndroidTV. On my system, the completed recording plays back directly (no HLS re-mux) so I started investigating if there was something in the HLS flow that could be impeding the captions. I found that Emby uses ffmpeg to segment the incoming live TS stream but ffmpeg is not being used to create a master m3u8 playlist; it is just creating a chunk(segment) list. Is the ffmpeg chunk list passed directly to exoplayer? Or does Emby create a master m3u8 playlist that references the chunk list on its own? 
Reading here: https://github.com/androidx/media/issues/1526

It appears that master HLS tags are required to get exoplayer to properly use the closed caption information and master tags can only be present in a master m3u8 playlist. If the tags don't work, then according to the github thread, you can force your implementation of exoplayer to disable chunkless preparation and the CC info can be found from the stream. 

Does Emby have a master m3u8 playlist that the correct tags could be inserted into? Have these tweaks been tried before? 

 

Example Master CC tags:

#EXTM3U

#EXT-X-VERSION:3

#EXT-X-MEDIA:TYPE=CLOSED-CAPTIONS,GROUP-ID="hdhr_cc",NAME="English",DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="en",INSTREAM-ID="CC1"

#EXT-X-STREAM-INF:BANDWIDTH=15000000,CLOSED-CAPTIONS="hdhr_cc" chunk_file.m3u8