HDX MediaStream for Flash Feature Dynamic Blacklist Explained

Website Visitors:

There are certain situations in which HDX MediaStream for Flash failsfor certain Website URLs. This happens as a result of certain Web pages that have been designed to work in a way that is not compatible with our HDX architecture. These failures cannot be detected, so HDX has been designed to create and use a Dynamic Blacklist to remember Websites that provoke these failures. In these situations, the HDX feature falls back to server-side Flash rendering for the current browser tab that provoked the failure. Additionally, it uses server-side rendering for all future browser tabs that navigate to the failing URL Website.

Note: It appears that the number of Websites and Flash applications that might experience these problems is small and limited.

Dynamic Blacklist Triggers

The following events cause an offending Website to be added to the user’s dynamic blacklist:

  • A failed attempt to fetch content from the client. Such as when a client device does not have access to the content server.
  • An attempt to fetch content from a local file system path.
  • A crash or panic in the HDX MediaStream for Flash client (HDX Event Viewer ID: 46)
  • A crash or panic in the HDX MediaStream for Flash server (HDX Event Viewer ID: 42)

When HDX MediaStream for Flash experiences any of the above listed events, the following actions occur:

  1. The current top-level URL of the offending browser tab is refreshed, and HDX MediaStream for Flash is no longer used for the reloaded page.
  2. The current top-level URL of the offending browser tab is added to the user’s dynamic blacklist. If the user browses to that URL for a period of time in the future (24 hours), then the HDX MediaStream for Flash feature will not be used.
  3. The appropriate event log is generated on the XenApp server (If the HDX GPO for server side event logging is enabled).

Dynamic Blacklist Registry Paths

The dynamic blacklist additions are placed in a per-user registry location as follows: These registry paths contain a list:

For Internet Explorer 7 and Internet Explorer 8 in non-protected mode:


For Internet Explorer 8 in protected mode, (Note: user SID specific path):


Flash URL blacklist

This setting specifies Web sites whose Flash content is rendered on the server. Flash content on unlisted Web sites is rendered on the user device.

When adding this setting to a policy, make sure the Flash acceleration setting is present and set to Enabled. Otherwise, Web sites listed in the URL blacklist are ignored.

Listed URL strings do not need the http:// or https:// prefix. These prefixes are ignored if found. Wildcards (*) are valid at the beginning and end of a URL.

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