f9cefbfec4 made it so mp_ass_flush_old_events() is continously called on
subtitles with unknown duration, without explaining why, breaking
sub-seek/step -1 with a VO (the issue does not occur when showing
subtitles in the terminal because get_bitmaps() is not called). I don't
experience any issue after removing the call, so delete it to fix these
commands.
After removing that, you can sub-seek -1 once after regular playback,
but not after seeking and thus not multiple times in a row. This is
caused by a714f8e928 which fixed subtitles with unknown duration being
duplicated when seeking with a VO (it does not happen in the terminal)
by clearing old lines on seeks, which broke sub-seek -1 and sub-step -1
in a second way after any seek. The proper fix is to remove the line
ctx->num_seen_packets = 0 for subtitles with unknown duration instead,
which lets decode() return early when a line has already been shown.
Having removed these 2 lines, I also removed sd->preload_ok = false, and
thus the whole conditional, since according to sub/sd.h preload_ok only
needs to be set to false when old subtitles are discarded, and they are
no longer discarded,
The bug can be reproduced with
mpv --sub-file=<(curl 'https://music.xianqiao.wang/neteaseapiv2/lyric?id=1399616170' | jq -r .lrc.lyric) 'https://www.youtube.com/watch?v=dQw4w9WgXcQ'
0f2370476b