Microsoft Windows CE 3.0  

Static and Streaming Sound Buffers

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When you create a secondary sound buffer, you specify whether it is a static sound buffer or a streaming sound buffer. A static buffer contains a complete sound in memory. A streaming buffer holds only a portion of a sound, such as 3 seconds of data from a 15-second bit of voice dialog. When using a streaming sound buffer, your application must periodically write new data to the buffer.

If a sound device has on-board sound memory, DirectSound attempts to place static buffers in the hardware memory. These buffers can then take advantage of hardware mixing, and the processing system incurs little or no overhead to mix these sounds. This is particularly useful for sounds your application plays repeatedly, because the sound data must be downloaded only once to the hardware memory.

Streaming buffers are generally located in main system memory to allow efficient writing to the buffer, although you can use hardware mixing on peripheral component interconnect (PCI) machines or other fast buses.

DirectSound distinguishes between static and streaming buffers in order to optimize performance, but it does not restrict how you can use the buffer. If a streaming buffer is big enough, there is nothing to prevent you from writing an entire sound to it in one chunk. In fact, if you do not intend to use the sound more than once, it can be more efficient to use a streaming buffer because by doing so you eliminate the step of downloading the data to hardware memory.

Your application may attempt to explicitly locate buffers in hardware or software. If you attempt to create a hardware buffer and there is insufficient memory or mixing capacity, the buffer creation request fails. Many existing sound cards do not have any on-board memory or mixing capacity, so no hardware buffers can be created on these devices.

For more information, see Creating Secondary Buffers.

 Last updated on Tuesday, May 18, 2004

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