int ff_init_poc(H264Context *h, int pic_field_poc[2], int *pic_poc)
{
    const int max_frame_num = 1 << h->sps.log2_max_frame_num;
    int field_poc[2];

    h->frame_num_offset = h->prev_frame_num_offset;
    if (h->frame_num < h->prev_frame_num)
        h->frame_num_offset += max_frame_num;

    if (h->sps.poc_type == 0) {
        const int max_poc_lsb = 1 << h->sps.log2_max_poc_lsb;

        if (h->poc_lsb < h->prev_poc_lsb &&
            h->prev_poc_lsb - h->poc_lsb >= max_poc_lsb / 2)
            h->poc_msb = h->prev_poc_msb + max_poc_lsb;
        else if (h->poc_lsb > h->prev_poc_lsb &&
                 h->prev_poc_lsb - h->poc_lsb < -max_poc_lsb / 2)
            h->poc_msb = h->prev_poc_msb - max_poc_lsb;
        else
            h->poc_msb = h->prev_poc_msb;
        field_poc[0] =
        field_poc[1] = h->poc_msb + h->poc_lsb;
        if (h->picture_structure == PICT_FRAME)
            field_poc[1] += h->delta_poc_bottom;
    } else if (h->sps.poc_type == 1) {
        int abs_frame_num, expected_delta_per_poc_cycle, expectedpoc;
        int i;

        if (h->sps.poc_cycle_length != 0)
            abs_frame_num = h->frame_num_offset + h->frame_num;
        else
            abs_frame_num = 0;

        if (h->nal_ref_idc == 0 && abs_frame_num > 0)
            abs_frame_num--;

        expected_delta_per_poc_cycle = 0;
        for (i = 0; i < h->sps.poc_cycle_length; i++)
            expected_delta_per_poc_cycle += h->sps.offset_for_ref_frame[i];

        if (abs_frame_num > 0) {
            int poc_cycle_cnt          = (abs_frame_num - 1) / h->sps.poc_cycle_length;
            int frame_num_in_poc_cycle = (abs_frame_num - 1) % h->sps.poc_cycle_length;

            expectedpoc = poc_cycle_cnt * expected_delta_per_poc_cycle;
            for (i = 0; i <= frame_num_in_poc_cycle; i++)
                expectedpoc = expectedpoc + h->sps.offset_for_ref_frame[i];
        } else
            expectedpoc = 0;

        if (h->nal_ref_idc == 0)
            expectedpoc = expectedpoc + h->sps.offset_for_non_ref_pic;

        field_poc[0] = expectedpoc + h->delta_poc[0];
        field_poc[1] = field_poc[0] + h->sps.offset_for_top_to_bottom_field;

        if (h->picture_structure == PICT_FRAME)
            field_poc[1] += h->delta_poc[1];
    } else {
        int poc = 2 * (h->frame_num_offset + h->frame_num);

        if (!h->nal_ref_idc)
            poc--;

        field_poc[0] = poc;
        field_poc[1] = poc;
    }

    if (h->picture_structure != PICT_BOTTOM_FIELD)
        pic_field_poc[0] = field_poc[0];
    if (h->picture_structure != PICT_TOP_FIELD)
        pic_field_poc[1] = field_poc[1];
    *pic_poc = FFMIN(pic_field_poc[0], pic_field_poc[1]);

    return 0;
}

Unknown