Writeback metadata using the FotowebSteamWrapper

fotoweb-write-back-metadata.php

if ($file_wrapper = file_stream_wrapper_get_instance_by_uri($file->uri)) {
  // Specifiy the Fotoweb property to update.
  $metadata_key_to_update = 60;

  // Set the new value.
  $file->metadata['asset_metadata'][$metadata_key_to_update]['value'] = 'My new caption';

  // Update the metadata and trigger the file_save, which could
  // overwrite the $file->metadata with the actual asset metadata
  // for data consistency.
  if ($file_wrapper->update_metadata(array($metadata_key_to_update => $file->metadata['asset_metadata'][$metadata_key_to_update]))) {
    file_save($file);
  }
}