#11208: HLS append segments to VTT playlist
-------------------------------------+-------------------------------------
Reporter: jb_alvarado | Type: defect
Status: new | Priority: normal
Component: | Version:
undetermined | unspecified
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Summary of the bug:
When we use the hls_flag `append_list+omit_endlist` in combination with a
Webvtt file, the result playlists differs in behavior, which makes the
subtitle useless and ffmpeg write errors.
One issue is, that in the subtitle playlist stream_vtt.m3u8 is the
`#EXT-X-DISCONTINUITY` tag missing.
Second issue is, that the end tag is written to the subtitle file, so the
flag `omit_endlist` get ignored.
The third issue is, when writing again to the same playlist, segments are
not correctly added. Instead the new segments are added, but the old ones
are replaced by a dot, like:
```
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:6
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:6.000000,
.
#EXTINF:6.000000,
.
#EXT-X-DISCONTINUITY
#EXTINF:6.000000,
stream2.vtt
#EXTINF:6.000000,
stream3.vtt
#EXT-X-ENDLIST
```
How to reproduce:
{{{
% ffmpeg -hide_banner -i video.mp4 -i subtitle.vtt -map "0:v" -map "0:a"
-map "1:s" -t 12 -c:v libx264 -crf 23 -preset faster -tune zerolatency
-c:a aac -ar 44100 -b:a 128k -flags +cgop -f hls -hls_time 6
-hls_list_size 60 -hls_flags append_list+delete_segments+omit_endlist
-var_stream_map "v:0,a:0,s:0,sgroup:subs,language:de,default:YES"
-master_pl_name master.m3u8 -hls_segment_filename stream-%d.ts stream.m3u8
# Run the command again and open the stream_vtt.m3u8 file and see the
problem.
# ffmpeg git-2024-09-26-f43916e
# built on fedora 40
}}}
The first issues I was able to fix and I sendet a patch to the devel
mailing list, the second issue with the end tag is also not big problem,
but the third one is to difficult for me.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/11208>
FFmpeg <https://ffmpeg.org>
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