void
MetaMap::writeMeta(std::ostream &os) const
{
    // Write out the number of metadata items we have in the map. Note that we
    // save as Index32 to save a 32-bit number. Using size_t would be platform
    // dependent.
    Index32 count = static_cast<Index32>(metaCount());

    // Disable writing of any metadata that does not fit into 31-bits
    std::vector<int8_t> valid(size_t(count), int8_t(1));
    for (ConstMetaIterator iter = beginMeta(), int i = 0; iter != endMeta(); ++iter, ++i) {
        if (iter->second->size() >= math::Pow(2, 31) - 1) {
            valid[i] = false;
            count--;
        }
    }

    os.write(reinterpret_cast<char*>(&count), sizeof(Index32));

    // Iterate through each metadata and write it out.
    for (ConstMetaIterator iter = beginMeta(), int i = 0; iter != endMeta(); ++iter, ++i) {
        // Don't write out metadata that doesn't fit into 32-bits
        if (!valid[i])  continue;

        // Write the name of the metadata.
        writeString(os, iter->first);

        // Write the type name of the metadata.
        writeString(os, iter->second->typeName());

        // Write out the metadata value.
        iter->second->write(os);
    }
}