| Multimedia and XenApp - what you can and can't do |
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| Written by Andrew Wood | |
| Sunday, 28 March 2010 | |
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Often as a Citrix Admin you'll be asked about enabling video in your XenApp farm. Historically, audio and video in Citrix/Terminal Services environment wasn't that pretty - especially if your users were in remote offices. User experience was often poor and/or the delivering multimedia meant that there was an extra demand on the servers. However - Citrix have kept adding functionality - the core ICA protocol has a number of technologies that compliment it to improve the multimedia experience. If you need to deliver better graphics and multimedia, what can be done? Bear in mind in many instances you can simply host the multimedia service on your XenApp server: if your users are LAN based for example, most video formats aren’t going to hose the performance of the server. Just because its video doesn't mean its always going to be bad - test it first in your environment. However, its fair to say if your users are on a WAN their experience of video is going to be choppy – with some audio issues.
Speedscreen Progressive Display Speedscreen Progressive Display, introduced in XenApp 4.5, is one of Citrix's primary technologies behind server-rendered multimedia delivery. It is not only important in the context of 2D and 3D 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. You can manage Progressive Display settings through your Citrix Connection Policies.
You can look at selecting different levels of compression to provide a good balance between frame rate and the visual quality of each frame given the effective network bandwidth that's available: so it does need some testing. While there's plenty of bandwidth to deliver a high frame rate and high frame quality on a LAN, on a remote connection you can’t choose an image quality setting that's bandwidth intensive. With Progressive Display you can modify your Image Acceleration Policy to use the High Compression setting or, if you’ve lower bandwidth you might prefer to use Very High Compression – there’s even a ‘I’ve a bit of string for my remote comms - set compression to stun’ in the form of 'heavyweight compression' . As its a policy setting, you can configure a policy that only enables this feature for your remote devices. These changes come at a “cost” – they’ll all bump up CPU demand on the server but, it can enable you to get a better multimedia experience over a WAN connection. Content Redirection There are alternatives to using Progressive Display. “Content Redirection” options use the end device for rendering content (and so taking load off of the server) but only for certain media types. HDX Multimedia for Flash, for example, works only for Adobe Flash – not for QuickTime and Silverlight. Also, if network latency is high the default fall back for HDX Multimedia is to go back to server-side redirection: so you could do a lot of effort and end up having it delivered from the server anyways. Server to Client Content Redirection What happens if you always want to use the end device's resources? If you’re running published apps, you could enable Server to Client Content Redirection. When you enable server to client content redirection, embedded URLs are intercepted on the server running Citrix Presentation Server and sent to the client. The user’s locally installed browser is used to render the URL: users cannot disable this feature. This gives you the facility to redirect http, https and real player,quicktime and microsoft’s media streaming to the local client’s browser. Here’s a document that explains how Server to Client Content Redirection is configured - http://support.citrix.com/article/CTX113457 . Given you've redirected traffic to your user's browser you've now got to open up web access to those devices. Even if we put aside questions around ‘are your devices up-to-date with codecs, IE security updates and add-ins’, is your branch link going to be able to cope with that extra content demand? Potentially the increased web traffic may impact on your existing ICA use: also, now your browser is local, is that going to impact on anything else? Intranet access? Printing from web pages? Integration with your Sharepoint? Server to Client Content Redirection will always redirect content, but it doesn't offer a full range of multimedia redirection, and redireting web content can in itself cause experience problems integrating with other applications.HDX MediaStream Server to Client content redirection was the first 'client resource use' offering but now, we’ve the wonders of HDX Mediastream. – which can appear as SpeedScreen Multimedia Acceleration in your Citrix Farm settings. HDX MediaStream has a server and a client side component. From the server, the compressed multimedia information is sent directly to the end device in its native format. On the client side, the multimedia stream is rendered and played back on the end device. Unlike Server to Client Content Redirection you don't use the local browser - rather the conent playback component is 'embedded' into the published application. This benefits in easier integration of the published application's browser with other other applications hosted on the XenApp Servers while still using the processing of the client to render the video. From XenApp 4.5 FP2 this feature is enabled by default (so you shouldn’t have to do anything on the Citrix servers)
How do you know its working? When HDX MediaStream is working, a black rectangle will quickly flash by as the video begins to play – although the media player appears to start on the citrix server – the content is delivered from the client. Client side support for these featuresis available in win32 v11, win ce v10 and Linux x86 v11. And if yo're really not sure that its working here’s a document on Troubleshooting HDX MediaStream - http://support.citrix.com/article/CTX104912 . HDX Mediastream deals with a number of different video formats - however not all multimedia is video. For Adobe Flash based content there is a specific HDX Mediastream for Flash component. For setting this up, check out http://support.citrix.com/article/CTX124190 .Not sure if you've configured it correctly? There is a tool available for verifying the whole shebang – which you can get here: http://hdxflash.codeplex.com/. When it is configured correctly the Flash stuff is pretty clever. It puts the Adobe Flash “in” the ‘server based’ browser session using the local device's Adobe Flash player: so the user's experience of Adobe Flash rendering is much better. With both these features, server CPU usage will be lower than if the video were being rendered on the server and Progressive display is enabled. Yet, both of these 'local resource use' features come at their own cost. Server to Client Content Redirection uses full local resources yet, doesn't redirect all content types and requires that the local device has internet access. HDX Mediastream allows for better delivery of multimedia while still retaining published applications and using the ICA channel but, if the client doesn't support the codec of the video being used, or isn't up-to-date with the Adobe Flash player version, or the network latency between the end device and the server becomes too high – its back to server side rendering. What Can be Done? Multimedia with XenApp isn't a Dark Art, but its not as easy as saying 'Abracadabra'. Its possible, using Progressive Display, to enhance the multimedia experience - even for remote users: yet this can come at a cost of increased CPU use. There are options to utilise client-side resources - from XenApp 4.5 you've Server to Client Content Redirection and HDX MediaStream but these technologies also have limitations for example, Server to Client Content Redirection moves traffic outside of ICA, HDX MediaStream can be disabled by high latency. While multimedia support with XenApp is improving and is possible, the maxim "any time, any place, any device" still has a number of caveats and it'll be interesting to see how RemoteFX will impact on that.
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