static int dirac_combine_frame(AVCodecParserContext *s, AVCodecContext *avctx,
                               int next, const uint8_t **buf, int *buf_size)
{
    int parse_timing_info = (s->pts == AV_NOPTS_VALUE &&
                             s->dts == AV_NOPTS_VALUE);
    DiracParseContext *pc = s->priv_data;

    if (pc->overread_index) {
        memmove(pc->buffer, pc->buffer + pc->overread_index,
               pc->index - pc->overread_index);
        pc->index         -= pc->overread_index;
        pc->overread_index = 0;
        if (*buf_size == 0 && pc->buffer[4] == 0x10) {
            *buf      = pc->buffer;
            *buf_size = pc->index;
            return 0;
        }
    }

    if (next == -1) {
        /* Found a possible frame start but not a frame end */
        void *new_buffer =
            av_fast_realloc(pc->buffer, &pc->buffer_size,
                            pc->index + (*buf_size - pc->sync_offset));
        if (!new_buffer)
            return AVERROR(ENOMEM);
        pc->buffer = new_buffer;
        memcpy(pc->buffer + pc->index, (*buf + pc->sync_offset),
               *buf_size - pc->sync_offset);
        pc->index += *buf_size - pc->sync_offset;
        return -1;
    } else {
        /* Found a possible frame start and a  possible frame end */
        DiracParseUnit pu1, pu;
        void *new_buffer = av_fast_realloc(pc->buffer, &pc->buffer_size,
                                           pc->index + next);
        if (!new_buffer)
            return AVERROR(ENOMEM);
        pc->buffer = new_buffer;
        memcpy(pc->buffer + pc->index, *buf, next);
        pc->index += next;

        /* Need to check if we have a valid Parse Unit. We can't go by the
         * sync pattern 'BBCD' alone because arithmetic coding of the residual
         * and motion data can cause the pattern triggering a false start of
         * frame. So check if the previous parse offset of the next parse unit
         * is equal to the next parse offset of the current parse unit then
         * we can be pretty sure that we have a valid parse unit */
        if (!unpack_parse_unit(&pu1, pc, pc->index - 13)                     ||
            !unpack_parse_unit(&pu, pc, pc->index - 13 - pu1.prev_pu_offset) ||
            pu.next_pu_offset != pu1.prev_pu_offset                          ||
            pc->index < pc->dirac_unit_size + 13LL + pu1.prev_pu_offset
        ) {
            pc->index              -= 9;
            *buf_size               = next - 9;
            pc->header_bytes_needed = 9;
            return -1;
        }

        /* All non-frame data must be accompanied by frame data. This is to
         * ensure that pts is set correctly. So if the current parse unit is
         * not frame data, wait for frame data to come along */

        pc->dirac_unit = pc->buffer + pc->index - 13 -
                         pu1.prev_pu_offset - pc->dirac_unit_size;

        pc->dirac_unit_size += pu.next_pu_offset;

        if ((pu.pu_type & 0x08) != 0x08) {
            pc->header_bytes_needed = 9;
            *buf_size               = next;
            return -1;
        }

        /* Get the picture number to set the pts and dts*/
        if (parse_timing_info && pu1.prev_pu_offset >= 13) {
            uint8_t *cur_pu = pc->buffer +
                              pc->index - 13 - pu1.prev_pu_offset;
            int pts = AV_RB32(cur_pu + 13);
            if (s->last_pts == 0 && s->last_dts == 0)
                s->dts = pts - 1;
            else
                s->dts = s->last_dts + 1;
            s->pts = pts;
            if (!avctx->has_b_frames && (cur_pu[4] & 0x03))
                avctx->has_b_frames = 1;
        }
        if (avctx->has_b_frames && s->pts == s->dts)
            s->pict_type = AV_PICTURE_TYPE_B;

        /* Finally have a complete Dirac data unit */
        *buf      = pc->dirac_unit;
        *buf_size = pc->dirac_unit_size;

        pc->dirac_unit_size     = 0;
        pc->overread_index      = pc->index - 13;
        pc->header_bytes_needed = 9;
    }
    return next;
}