Users see Content Transformation Error Exception when browsing YouTube
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Users see Content Transformation Error Exception when browsing YouTube


Article ID: 169396


Updated On:


Advanced Secure Gateway Software - ASG ProxySG Software - SGOS


When browsing videos on, users may receive the following exception page:

Content Transformation Error (transformation_error) 

Proxy cannot apply content transformation. 
This could be caused by a misconfiguration, or possibly a response with an unknown content encoding. 


YouTube has introduced support for Brotli encoding, which is not supported by the ProxySG at this time (April 6, 2017). See this Wikipedia entry to learn more about Brotli encoding.


Because SGOS does not understand Brotli encoding, you will need to disable support for it. There are two options for this: modify the client browser, or install policy on the Proxy. 

Disable Brotli Encoding Support in Google Chrome

  1. In the Chrome address bar, type chrome://flags/
  2. Search the page for Brotli Content-Encoding.
  3. Click the drop-down menu to select Disabled
  4. Restart the browser for the change to take effect.

disable brotli support in chrome

Disable Brotli Encoding Support in Mozilla Firefox

  1. In the Firefox address bar, type about:config and press enter.
  2. Enter into the search field.
  3. Double-click the entry and remove br from the list of supported encoding types.

disable brotli support in firefox



Alternatively, you can disable support for Brotli encoding just for YouTube in policy on the Proxy:

  1. Log in to the Management Console in your browser 
  2. Navigate to Configuration > Policy > Visual Policy Manager and click Launch
  3. In the VPM, click Edit > Add CPL Layer
  4. Add the following policy: 
define action ForceUncompressedResponse 
<Cache> action.ForceUncompressedResponse(yes) 
  1. Click Install Policy to commit this change to your configuration.