HDX MediaStream is our name for a set of Citrix technologies for delivering video and audio content from virtual desktops and hosted applications. The foundation of HDX MediaStream is the ability to deliver any media format from any media player over any network connection to any device. (Did I use the “any” word enough?) That’s what Server-Rendered Multimedia Delivery is all about. Then, on top of this solid foundation, we look for opportunities to achieve higher server scalability by offloading media processing to the user device when possible. For example, since Adobe Flash content is so prevalent and the Flash Player consumes quite a lot of CPU, last year we introduced HDX MediaStream Flash Redirection to complement our existing Windows Media Redirection.
Even for Flash and Windows Media, server-rendered multimedia delivery comes into play when network latency is too high for Flash redirection or effective bandwidth is too low for Windows media redirection. The SmartRendering feature of HDX Adaptive Orchestration selects the appropriate technology based on the dynamic network conditions at hand. Likewise, SmartRendering recognizes if the user device is not capable of client-side rendering.
Server-side multimedia delivery also supports alternative media formats and players such as QuickTime and Silverlight. The user experience for these media formats over a high bandwidth connection is very similar to client-side rendering, “just like local”. XenDesktop 4 supports an out-of-the-box frame rate of 24 fps (just like at the cinema) and can be adjusted to deliver a full 30 fps if required for certain demanding use cases.
So, how do you get the best performance out of server-rendered multimedia delivery? Here are my top three tips:
1. Configure Progressive Display to compress images in motion.
2. Use Branch Repeater when delivering video to remote locations.
3. Use the new High Definition audio codec.
Progressive Display is one of the primary technologies behind server-rendered multimedia delivery. I’ve blogged about Progressive Display in the past in the context of graphics and medical imaging, but it is also very important for video. Progressive Display recognizes images in motion (such as video) and applies more aggressive compression to this content than to stationary images. It works in conjunction with the Dynamic Frame Rate Capping feature introduced in XenDesktop 4 for users on low bandwidth connections.
The key to tuning Progressive Display for video delivery is to select a level of compression that provides a good balance between frame rate and the visual quality of each frame given the effective network bandwidth that’s available. On a LAN, there’s plenty of bandwidth to deliver both a high frame rate and high frame quality. But on a T1 link (1.5 Mbps), something’s gotta give. On that sort of connection you probably don’t want to choose an image quality setting that’s so bandwidth intensive it would leave you with a slide show. So that’s a great example of where your Image Acceleration Policy (configured in the Citrix Management Console) should use the High Compression setting. At 1.0 Mbps, you might prefer to use Very High Compression. If you’re willing to spend more CPU power on the server, Heavyweight Compression (arithmetic encoding) will produce the same image quality with even lower bandwidth consumption; or put another way, it enables you to get an even better multimedia experience over the same WAN connection.
What if bandwidth fluctuates during the user session? No problem. All bandwidth-related decisions are made dynamically, based on the latest network conditions.
HDX WAN Optimization (powered by Branch Repeater) works together with HDX MediaStream to improve video performance for branch office workers. One of the main benefits of using the Branch Repeater is that data is cached locally at the branch. Since branch office workers often need to watch the same training and corporate communications videos, the result is that they can be served by a smaller pipe than would otherwise be necessary, as highlighted in Citrix Consulting’s recent whitepaper on XenDesktop 4 bandwidth requirements for branch offices.
Lastly, a critical aspect of the overall user experience when viewing videos is the sound quality. XenDesktop 4 introduced new codec technology that delivers outstanding audio fidelity when viewing server-rendered videos. If you still have users with older versions of the Citrix online plug-in (ICA client), you should set the audio quality to Medium. But if your users have the 11.2 or 12.0 online plug-in for Windows or the 11.100 Citrix Receiver for Linux, then you can choose the High Definition audio setting for great sound using less than 100 Kbps of network bandwidth.
For more detail on how to configure HDX MediaStream server-rendered multimedia delivery, including additional tips on audio tuning, check out Citrix Knowledge Base article CTX124516.
Citrix Product Strategist, HDX