Stutter
The Source Engine uses a caching system, whereby the loading of certain resources is handled and managed on the fly, rather than in a single operation behind a traditional loading screen. Texture and sound data are the primary areas in which this occurs. Textures are loaded to memory but only moved to the system's video card when needed and audio files are loaded with an unusual "soundcache" system: only the first 0.125 seconds of each file are pre-cached, and the clip is used to cover the asynchronous buffering of the full sound file in the background when it is first requested.
Both systems keep data in the heap until there is no more room and older resources are flushed out, and when either is held up or otherwise slowed down the engine will either freeze or go into a temporary loop until the data arrives. 'Stuttering', or 'hitching' as it is sometimes known, is the result of these pauses.
While stutter can be caused by poor system performance, it has also been noted on hardware setups that should be more than powerful enough to cope with the data rate, and despite many theories, the precise cause remains unknown to the public even over two years since the engine's debut. Most solutions that have been found involve bypassing the caching system, as it cannot be directly disabled, or system-specific optimizations (e.g. driver updates).
When Half-Life 2 was first released and stuttering became a widely-known problem, community member Mark McWilliams set up a page covering the issue and Valve's communication and work on resolving it. [19] Several updates were released by Valve, the effects of which varied from complete fixes for some users to previously smooth systems becoming "infected" with the problem.
* Example (.WMV), showing a relatively low level of stutter. The hitches coincide with the drawing of new areas (a process that is by design not visible without debugging tools).
Most recently (February 7, 2006), changes to the Source engine were introduced alongside a beta test of Steam's Friends chat service, with the aim of 'narrowing down' the problem. [20] The update featured a limited implementation of Source's file streaming system (see above). Generally, the response was very positive.
Looping audio
The Source Engine suffers from an error whereby the asynchronous loading (see Stutter, above) of a new sound file will cause the engine to lock up with looping audio. Because of the nature of DirectX, once the engine enters such a state it will remain on the screen unless the user can blindly terminate the program, or reboots their computer. The error occurs in a standard Windows library associated with on-board sound cards, and in some cases can be resolved by decreasing DirectSound Acceleration.
Reports of looping audio crashes increased around the release of Episode One. While it is likely that the spike was simply because there was an unusually high number of people playing the game, changes to the engine, of which there were many for the game, cannot be ruled out. It has been noted that people who have been able to play Half-Life 2 without any crashes and audio errors in fact do find Episode 1 to be more prone to that problem. A steampowered.com forum thread is dedicated to discussing the problem and attempting to work out solutions, although the experience of the thread contributors indicates that most suggested workarounds and fixes do not remedy the problem.
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