libass processing flow

ass_fontselect_init
    ass_coretext_add_provider
    ass_fontconfig_add_provider
ass_render_frame
ass_render_event
ass_shaper_find_runs
ass_font_get_index: "Glyph 0x%X not found, selecting one more "
add_face
ass_font_select
│   select_font
│   │   get_substitutions
│   │   find_font
│   │   match_fonts: fill missing fonts to font list
│   │   │   ass_font_provider_add_font
│   │   │       ass_face_open
│   │   find_font
│   get_fallback