public string GetSongUrl(string externalId)
{
string format;
int databaseId, trackId;
ToDaap(externalId, out databaseId, out trackId, out format);
var database = this._client.Databases.FirstOrDefault(d => d.Id == databaseId);
var track = new Track();
track.SetId(trackId);
track.Format = format;
database.DownloadTrack(track, _tempFilename);
return _tempFilename;
}