Write Access to the Primary Buffer

The primary sound buffer outputs audio samples to the sound device. DirectSound provides direct write access to the primary buffer; however, this feature is useful for a very limited set of applications that require specialized mixing or other effects not supported by secondary buffers. Gaps in sound are difficult to avoid when an application writes directly to the primary buffer; those that access the primary buffer directly are subject to very stringent performance requirements.

A primary buffer is typically very small, so if your application writes directly to this kind of buffer, it must write blocks of data at short intervals in order to prevent the previous block in the buffer from repeating. During buffer creation, you cannot specify the size of the buffer and must accept the returned size once creation is complete.

When you obtain write access to a primary sound buffer, other DirectSound features become unavailable. Secondary buffers are not mixed and, consequently, hardware-acceleration mixing is unavailable. (When DirectSound mixes sounds from secondary buffers, it places the mixed audio data in the primary buffer.)

Most of your applications should use secondary buffers instead of directly accessing the primary buffer. Applications can write to a secondary buffer easily because the larger buffer size provides more time to write the next block of data, thereby minimizing the risk of gaps in the audio. Even if your application has simple audio requirements, such as using one stream of audio data that does not require mixing, it will achieve better performance by using a secondary buffer to play its audio data.