The content caching feature was added in WACS 0.9.1 and provides a vastly improved performance when WACS is used in a commercial site. It is also a pre-requisite of allowing facilities like video content streaming and embedded video players to work. Unlike all the other options discussed earlier in this chapter, this option has to be enabled on a per-set basis through manual creation of the cache for the specified set. If a cached version is not available, WACS defaults to handling downloads in the normal way through calling wacszip . It does not create a new cached copy.

The content caches are enabled by creating a content caching directory within your web server document tree and setting the contenti and contentv attributes within the fsloc section of the configuration. The URLs to retrieve them from are set in serveriurl and servervurl in the server section of the configuration file. The caches themselves are maintained using the wacscachectl tools with the wacsvidcomb tool used to create compilation videos from multi-part originals. A detailed discussion of how the architecture works are to be found in the Hosting chapter of the Administration Guide. Please refer to this for more details.

	Tip
	Further enhancements to the collection administration toolchain in WACS 0.9.2 mean that the web interface now offers limited access to the wacscachectl and the whole system, once configured, is much easier to use.

From an operational point of view, the content cache mechanism typically uses very little extra disc space when used for video files as a symbolic link is placed into the content cache directory tree pointing back to the original location of the video file. Only when it is used to make a combined playable clip from a multipart video sequence does it create an independant new video file that consumes additional storage space. In this case, this involves use of the wacsvidcomb command to create the new combined video file.

Streaming Video Content

With the content cacheing system enabled, it becomes possible to offer streaming video in conjunction with the appropriate plug-in support enabled within the web server. This is only possible when using direct access to the files as configured by wacscachectl. This is now offered as an option during new set markup, and future development work for WACS will include tool options to retro-enable it for previously created video sets. Content caching is currently available for two types of video files: Flash Video files (.flv) through the use of the mod_flvx plug-in, and more usefully for most sites for h264/mp4 files using the mod_h264_streaming plug-in module.

	Warning
	Check the licenses on these plug-ins before utilising them on a commercial site - at least one of them has some restriction on free use

Once these modules are enabled within your Apache web server, suitable aware clients such as videolan.org's VLC video player will be able to instantly play and seek around in video clips hosted on WACS. Additionally embedded video players within suitable HTML5 conformant web sites should also be able to do so. There is no additional configuration of either these plug-in modules or of WACS itself beyond those discussed already that is needed to make use of them.

	Note
	As of WACS 0.9.2, none of the WACS standard web apps use HTML5 embedded players, but this is expected to change for the next release of WACS as we start making active use of all the new technologies for improved performance encorporated in the WACS 0.9.x release series.