What is the reason for the disappearance of subtitles in this m3u8 format stream after ffmpeg encoding
pipe:///usr/bin/ffmpeg -i "https://liveorigin01.hbogoasia.com:8443/origin/live/MSIA/index.m3u8" -vcodec copy -acodec copy -map 0 -c copy -f mpegts pipe:1
#EXTM3U
#EXT-X-VERSION:7
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audiod",NAME="audio_eng",DEFAULT=YES,AUTOSELECT=YES,CHANNELS="2",LANGUAGE="eng",URI="5.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audiod",NAME="audio_mal",DEFAULT=NO,AUTOSELECT=YES,CHANNELS="2",LANGUAGE="mal",URI="6.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audiod",NAME="audio_chi",DEFAULT=NO,AUTOSELECT=YES,CHANNELS="2",LANGUAGE="chi",URI="7.m3u8"
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="eng",DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="eng",URI="8.m3u8"
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="man",DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="man",URI="9.m3u8"
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="mal",DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="mal",URI="10.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=687256,AVERAGE-BANDWIDTH=687256,CODECS="avc1.640015,mp4a.40.2",PROGRAM-ID=1,RESOLUTION=480x270,AUDIO="audiod",SUBTITLES="subs"
1.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1147048,AVERAGE-BANDWIDTH=1147048,CODECS="avc1.64001e,mp4a.40.2",PROGRAM-ID=1,RESOLUTION=640x360,AUDIO="audiod",SUBTITLES="subs"
2.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=1964424,AVERAGE-BANDWIDTH=1964424,CODECS="avc1.64001f,mp4a.40.2",PROGRAM-ID=1,RESOLUTION=960x540,AUDIO="audiod",SUBTITLES="subs"
3.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=3803560,AVERAGE-BANDWIDTH=3803560,CODECS="avc1.640028,mp4a.40.2",PROGRAM-ID=1,RESOLUTION=1920x1080,AUDIO="audiod",SUBTITLES="subs"
4.m3u8
