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HLS stream subtitles

Im working with HLS HD streams via live channels .
Everythings works fine , outstanding my requirements ,
but i need to include a subtitle stream with the video and audio.
it is possible to use LIVE subtitles in HLS ?
these subtitles streams come along the audio and video , generally in DVB subtitle format.

ffmpeg takes this from original stream

Stream #0:12[0x580]: Video: h264 ([27][0][0][0] / 0x001B), 29.97 tbr, 90k tbn
Stream #0:13[0x581]: Audio: ac3 ([6][0][0][0] / 0x0006), 48000 Hz, 5.1(side), s16, 384 kb/s
Stream #0:14[0xbc2](spa): Subtitle: dvb_subtitle ([6][0][0][0] / 0x0006)

and convert audio and video smoothly to hls.

but many channels have no sense without subtitles.
maybe putting a first instance of ffmpeg in order to burn subtitles into original video stream ,
but this require more complex process and probably another machine to do this first.
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12 Replies

Re: HLS stream subtitles

interesting article :

http://www.overdigital.com/2011/12/27/h ... ould-care/

maybe implementation of HDS will be the answer to the subtitle quiz.

this is useful for impaired people.
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Anonymous
Level 8

Re: HLS stream subtitles

Hi Hugo,

We currently have support for subtitles on live and on-demand SmoothStreaming and on-demand HLS. This is all in SMPTE-TT format. We're looking at supporting 608-format closed captions for live HLS, but I don't have any info on potential timing for you at this time
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Re: HLS stream subtitles

ok. any clue to catch info about "support for subtitles on live and on-demand SmoothStreaming and on-demand HLS. This is all in SMPTE-TT format. " ?
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bosborne
Level 7

Re: HLS stream subtitles

I'm looking for details on this as well.
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bosborne
Level 7

Re: HLS stream subtitles

Has there been any update on this? Thanks
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Highlighted
RokuKevin
Level 7

Re: HLS stream subtitles

In order to get closed captioning working, all you have to do is set the subtitleUrl content meta data parameter to the TTML url and turn on and off the captions using the new roVideoScreen method ShowSubtitle( Boolean enable).

--Kevin
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bosborne
Level 7

Re: HLS stream subtitles

Okay, so we need to specify an external TTML file, and Roku doesn't support embedded TTML in Smooth or HLS?
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Re: HLS stream subtitles

ok. i solve this issue this a lot of processors. first decode to mpeg2 , then merge the dvb subs , then recode to h264 ,
works well , even with variable fps (crf=20) , with a final resolution of 850x480 (from 1280x720) in realtime , via an i7 6cores 3.4Ghz.
next week i post the data.
i test some decoders , works best with ffmpeg , but vlc is more stable chopping HLS.
ffmpeg 10.5 only (at least in centos 6.3 64bits), other versions do not work properly selecting streams from dvb multicast udp.

maybe i need to make another post : clues to select reverse-forward ?
on a simple m3u8 list with 8 segments , ever start at the oldest, giving no chance to point to the newest , or at least the subsequent.
theres may be an interesting point . the proccess of encoding takes 99% of processing , while chopping takes only 0.3%
so , with two (or more , via unix tee) you can have (and offer) many m3u8 lists from same "live" HLS with only 9sec of delay (3segments od 3 sec),
or "recorded" HLS from past hour and so on. i tested up to 1440 segments of 1 min , with m3u8 lists of last 60 - 120 - 180 -etc segments .

but i cant jump from segment to another , in order to forward-rewind the "live" HLS.
it is possible?
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bosborne
Level 7

Re: HLS stream subtitles

Just wanted to follow up on my previous question:

"Okay, so we need to specify an external TTML file, and Roku doesn't support embedded TTML in Smooth or HLS?"
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