public async Task <Stream> GetStreamAsync(string url, TimeSpan?duration = null)
{
string filename = _md5Helper.MD5(url);
string filepath = Path.Combine(_diskCache.BasePath, filename);
var stream = _diskCache.TryGetStream(filename);
if (stream != null)
{
return(stream);
}
var data = await DownloadAndCacheAsync(url, filename, filepath, duration).ConfigureAwait(false);
return(new MemoryStream(data));
}