static void mov_create_chapter_track(AVFormatContext *s, int tracknum)
{
    MOVMuxContext *mov = s->priv_data;
    MOVTrack *track = &mov->tracks[tracknum];
    AVPacket pkt = { .stream_index = tracknum, .flags = AV_PKT_FLAG_KEY };
    int i, len;

    track->mode = mov->mode;
    track->tag = MKTAG('t','e','x','t');
    track->timescale = MOV_TIMESCALE;
    track->enc = avcodec_alloc_context3(NULL);
    track->enc->codec_type = AVMEDIA_TYPE_SUBTITLE;

    for (i = 0; i < s->nb_chapters; i++) {
        AVChapter *c = s->chapters[i];
        AVDictionaryEntry *t;

        int64_t end = av_rescale_q(c->end, c->time_base, (AVRational){1,MOV_TIMESCALE});
        pkt.pts = pkt.dts = av_rescale_q(c->start, c->time_base, (AVRational){1,MOV_TIMESCALE});
        pkt.duration = end - pkt.dts;

        if ((t = av_dict_get(c->metadata, "title", NULL, 0))) {
            len = strlen(t->value);
            pkt.size = len+2;
            pkt.data = av_malloc(pkt.size);
            AV_WB16(pkt.data, len);
            memcpy(pkt.data+2, t->value, len);
            ff_mov_write_packet(s, &pkt);
            av_freep(&pkt.data);
        }
    }
}