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Caching and Proxying On-Demand Streams

  • Article

Unlike a live broadcast, on-demand content has been archived and indexed is available on demand. That is, the content is stored in a fixed file that the client can control during playback. Each requested on-demand stream requires a unique connection to the server, and each can be controlled by the client. That is, a client can start, stop, and seek within an on-demand stream.

When a client requests content, the cache plug-in typically checks local storage. If the content exists locally and has not expired, the plug-in requests that the server deliver the content to the client.

If the content is not stored locally or has expired, the cache plug-in can direct the cache server to open a data path to the origin server and begin downloading the content. Also, the cache server can perform any of the following actions.

  • Deny the client access to the content.

  • Redirect the client to an alternate proxy server or URL.

  • Redirect the client to an alternate proxy server or URL while downloading the content from the origin server into local cache.

  • Open two data paths to the origin server. One path proxies the content to the client. The other path downloads the content into local storage.

  • Proxy the stream on demand.

To avoid unauthorized access, a Windows Media proxy server does not cache content from any upstream server that issues an authentication challenge. If the cache plug-in requests that the content be cached, the cache proxy server rejects the request. Furthermore, the WMS_DATA_ CONTAINER_VERSION_ALLOW_PROXY_CACHING flag must be set. The flags are stored in a content information context that is downloaded with the content. Your plug-in can retrieve the flags by using the GetCacheFlags method on the IWMSDataContainerVersion interface.

To determine whether the content requested by the client is of the on-demand type, a cache plug-in can call GetContentInformation on the IWMSCacheProxyServer interface.

The Windows Media server queries the origin server for information about the requested content and responds to the plug-in by calling OnGetContentInformation on the IWMSCacheProxyServerCallback interface.

The server returns a pointer to a Cache Content Information Context. If the WMS_CACHE_CONTENT_INFORMATION_CONTENT_TYPE field contains WMS_CACHE_CONTENT_TYPE_BROADCAST, the content is a broadcast. If the broadcast flag is not set, the content is on-demand.

Note

   The WMS_CACHE_CONTENT_INFORMATION_CONTENT_TYPE field can contain any combination of the flags in the WMS_CACHE_CONTENT_TYPE_FLAGS enumeration type.

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