private string GetCacheFileName(string cacheKey, IFormatInfo outputFormat)
{
var inputBytes = Encoding.UTF8.GetBytes(cacheKey);
var hash = MD5.Create().ComputeHash(inputBytes);
var relativeUrl = new Guid(hash).ToString().Replace('-', '\\') + outputFormat.Extension;
return Path.Combine(m_cacheRoot.FullName, relativeUrl);
}