static int mxf_read_partition_pack(void *arg, AVIOContext *pb, int tag, int size, UID uid, int64_t klv_offset)
{
    MXFContext *mxf = arg;
    MXFPartition *partition, *tmp_part;
    UID op;
    uint64_t footer_partition;
    uint32_t nb_essence_containers;

    tmp_part = av_realloc_array(mxf->partitions, mxf->partitions_count + 1, sizeof(*mxf->partitions));
    if (!tmp_part)
        return AVERROR(ENOMEM);
    mxf->partitions = tmp_part;

    if (mxf->parsing_backward) {
        /* insert the new partition pack in the middle
         * this makes the entries in mxf->partitions sorted by offset */
        memmove(&mxf->partitions[mxf->last_forward_partition+1],
                &mxf->partitions[mxf->last_forward_partition],
                (mxf->partitions_count - mxf->last_forward_partition)*sizeof(*mxf->partitions));
        partition = mxf->current_partition = &mxf->partitions[mxf->last_forward_partition];
    } else {
        mxf->last_forward_partition++;
        partition = mxf->current_partition = &mxf->partitions[mxf->partitions_count];
    }

    memset(partition, 0, sizeof(*partition));
    mxf->partitions_count++;
    partition->pack_length = avio_tell(pb) - klv_offset + size;
    partition->pack_ofs    = klv_offset;

    switch(uid[13]) {
    case 2:
        partition->type = Header;
        break;
    case 3:
        partition->type = BodyPartition;
        break;
    case 4:
        partition->type = Footer;
        break;
    default:
        av_log(mxf->fc, AV_LOG_ERROR, "unknown partition type %i\n", uid[13]);
        return AVERROR_INVALIDDATA;
    }

    /* consider both footers to be closed (there is only Footer and CompleteFooter) */
    partition->closed = partition->type == Footer || !(uid[14] & 1);
    partition->complete = uid[14] > 2;
    avio_skip(pb, 4);
    partition->kag_size = avio_rb32(pb);
    partition->this_partition = avio_rb64(pb);
    partition->previous_partition = avio_rb64(pb);
    footer_partition = avio_rb64(pb);
    partition->header_byte_count = avio_rb64(pb);
    partition->index_byte_count = avio_rb64(pb);
    partition->index_sid = avio_rb32(pb);
    avio_skip(pb, 8);
    partition->body_sid = avio_rb32(pb);
    if (avio_read(pb, op, sizeof(UID)) != sizeof(UID)) {
        av_log(mxf->fc, AV_LOG_ERROR, "Failed reading UID\n");
        return AVERROR_INVALIDDATA;
    }
    nb_essence_containers = avio_rb32(pb);

    if (partition->this_partition &&
        partition->previous_partition == partition->this_partition) {
        av_log(mxf->fc, AV_LOG_ERROR,
               "PreviousPartition equal to ThisPartition %"PRIx64"\n",
               partition->previous_partition);
        /* override with the actual previous partition offset */
        if (!mxf->parsing_backward && mxf->last_forward_partition > 1) {
            MXFPartition *prev =
                mxf->partitions + mxf->last_forward_partition - 2;
            partition->previous_partition = prev->this_partition;
        }
        /* if no previous body partition are found point to the header
         * partition */
        if (partition->previous_partition == partition->this_partition)
            partition->previous_partition = 0;
        av_log(mxf->fc, AV_LOG_ERROR,
               "Overriding PreviousPartition with %"PRIx64"\n",
               partition->previous_partition);
    }

    /* some files don't have FooterPartition set in every partition */
    if (footer_partition) {
        if (mxf->footer_partition && mxf->footer_partition != footer_partition) {
            av_log(mxf->fc, AV_LOG_ERROR,
                   "inconsistent FooterPartition value: %"PRIu64" != %"PRIu64"\n",
                   mxf->footer_partition, footer_partition);
        } else {
            mxf->footer_partition = footer_partition;
        }
    }

    av_log(mxf->fc, AV_LOG_TRACE,
            "PartitionPack: ThisPartition = 0x%"PRIX64
            ", PreviousPartition = 0x%"PRIX64", "
            "FooterPartition = 0x%"PRIX64", IndexSID = %i, BodySID = %i\n",
            partition->this_partition,
            partition->previous_partition, footer_partition,
            partition->index_sid, partition->body_sid);

    /* sanity check PreviousPartition if set */
    //NOTE: this isn't actually enough, see mxf_seek_to_previous_partition()
    if (partition->previous_partition &&
        mxf->run_in + partition->previous_partition >= klv_offset) {
        av_log(mxf->fc, AV_LOG_ERROR,
               "PreviousPartition points to this partition or forward\n");
        return AVERROR_INVALIDDATA;
    }

    if      (op[12] == 1 && op[13] == 1) mxf->op = OP1a;
    else if (op[12] == 1 && op[13] == 2) mxf->op = OP1b;
    else if (op[12] == 1 && op[13] == 3) mxf->op = OP1c;
    else if (op[12] == 2 && op[13] == 1) mxf->op = OP2a;
    else if (op[12] == 2 && op[13] == 2) mxf->op = OP2b;
    else if (op[12] == 2 && op[13] == 3) mxf->op = OP2c;
    else if (op[12] == 3 && op[13] == 1) mxf->op = OP3a;
    else if (op[12] == 3 && op[13] == 2) mxf->op = OP3b;
    else if (op[12] == 3 && op[13] == 3) mxf->op = OP3c;
    else if (op[12] == 64&& op[13] == 1) mxf->op = OPSONYOpt;
    else if (op[12] == 0x10) {
        /* SMPTE 390m: "There shall be exactly one essence container"
         * The following block deals with files that violate this, namely:
         * 2011_DCPTEST_24FPS.V.mxf - two ECs, OP1a
         * abcdefghiv016f56415e.mxf - zero ECs, OPAtom, output by Avid AirSpeed */
        if (nb_essence_containers != 1) {
            MXFOP op = nb_essence_containers ? OP1a : OPAtom;

            /* only nag once */
            if (!mxf->op)
                av_log(mxf->fc, AV_LOG_WARNING,
                       "\"OPAtom\" with %"PRIu32" ECs - assuming %s\n",
                       nb_essence_containers,
                       op == OP1a ? "OP1a" : "OPAtom");

            mxf->op = op;
        } else
            mxf->op = OPAtom;
    } else {
        av_log(mxf->fc, AV_LOG_ERROR, "unknown operational pattern: %02xh %02xh - guessing OP1a\n", op[12], op[13]);
        mxf->op = OP1a;
    }

    if (partition->kag_size <= 0 || partition->kag_size > (1 << 20)) {
        av_log(mxf->fc, AV_LOG_WARNING, "invalid KAGSize %"PRId32" - guessing ",
               partition->kag_size);

        if (mxf->op == OPSONYOpt)
            partition->kag_size = 512;
        else
            partition->kag_size = 1;

        av_log(mxf->fc, AV_LOG_WARNING, "%"PRId32"\n", partition->kag_size);
    }

    return 0;
}