clpi_lookup_spn(CLPI_CL *cl, uint32_t timestamp, int before, uint8_t stc_id)
{
    CLPI_EP_MAP_ENTRY *entry;
    CLPI_CPI *cpi = &cl->cpi;
    int ii, jj;
    uint32_t coarse_pts, pts; // 45khz timestamps
    uint32_t spn, coarse_spn, stc_spn;
    int start, end;
    int ref;

    if (cpi->num_stream_pid < 1 || !cpi->entry) {
        if (before) {
            return 0;
        }
        return cl->clip.num_source_packets;
    }

    // Assumes that there is only one pid of interest
    entry = &cpi->entry[0];

    // Use sequence info to find spn_stc_start before doing
    // PTS search. The spn_stc_start defines the point in
    // the EP map to start searching.
    stc_spn = _find_stc_spn(cl, stc_id);
    for (ii = 0; ii < entry->num_ep_coarse; ii++) {
        ref = entry->coarse[ii].ref_ep_fine_id;
        if (entry->coarse[ii].spn_ep >= stc_spn) {
            // The desired starting point is either after this point
            // or in the middle of the previous coarse entry
            break;
        }
    }
    if (ii >= entry->num_ep_coarse) {
        return cl->clip.num_source_packets;
    }
    pts = ((uint64_t)(entry->coarse[ii].pts_ep & ~0x01) << 18) +
          ((uint64_t)entry->fine[ref].pts_ep << 8);
    if (pts > timestamp && ii) {
        // The starting point and desired PTS is in the previous coarse entry
        ii--;
        coarse_pts = (uint32_t)(entry->coarse[ii].pts_ep & ~0x01) << 18;
        coarse_spn = entry->coarse[ii].spn_ep;
        start = entry->coarse[ii].ref_ep_fine_id;
        end = entry->coarse[ii+1].ref_ep_fine_id;
        // Find a fine entry that has bothe spn > stc_spn and ptc > timestamp
        for (jj = start; jj < end; jj++) {

            pts = coarse_pts + ((uint32_t)entry->fine[jj].pts_ep << 8);
            spn = (coarse_spn & ~0x1FFFF) + entry->fine[jj].spn_ep;
            if (stc_spn >= spn && pts > timestamp)
                break;
        }
        goto done;
    }

    // If we've gotten this far, the desired timestamp is somewhere
    // after the coarse entry we found the stc_spn in.
    start = ii;
    for (ii = start; ii < entry->num_ep_coarse; ii++) {
        ref = entry->coarse[ii].ref_ep_fine_id;
        pts = ((uint64_t)(entry->coarse[ii].pts_ep & ~0x01) << 18) +
                ((uint64_t)entry->fine[ref].pts_ep << 8);
        if (pts > timestamp) {
            break;
        }
    }
    // If the timestamp is before the first entry, then return
    // the beginning of the clip
    if (ii == 0) {
        return 0;
    }
    ii--;
    coarse_pts = (uint32_t)(entry->coarse[ii].pts_ep & ~0x01) << 18;
    start = entry->coarse[ii].ref_ep_fine_id;
    if (ii < entry->num_ep_coarse - 1) {
        end = entry->coarse[ii+1].ref_ep_fine_id;
    } else {
        end = entry->num_ep_fine;
    }
    for (jj = start; jj < end; jj++) {

        pts = coarse_pts + ((uint32_t)entry->fine[jj].pts_ep << 8);
        if (pts > timestamp)
            break;
    }

done:
    if (before) {
        jj--;
    }
    if (jj == end) {
        ii++;
        if (ii >= entry->num_ep_coarse) {
            // End of file
            return cl->clip.num_source_packets;
        }
        jj = entry->coarse[ii].ref_ep_fine_id;
    }
    spn = (entry->coarse[ii].spn_ep & ~0x1FFFF) + entry->fine[jj].spn_ep;
    return spn;
}