.long_name = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
.extensions = "vtt",
.mime_type = "text/vtt",
+ .flags = AVFMT_VARIABLE_FPS | AVFMT_TS_NONSTRICT,
.subtitle_codec = AV_CODEC_ID_WEBVTT,
.write_header = webvtt_write_header,
.write_packet = webvtt_write_packet,