Open Sound System
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The exact purpose of this capability is currently undefined and it should not be used by any applications. At this moment some buggy applications incorrectly require this capability. For this reason it's reported with practically all devices which is definitely not the original idea.
Sometimes in the future (if the above misuse problem ever gets solved) this capability will be used to indicate devices that support some interface for finding out the exact latency values. This capability has nothing to do with "low" latencies. It just means that the device is able to tell the exact latencies to the application. The exact implementation is known yet.
Don't use this capability for any porposes. If your application uses it, please remove it immediately. OSS will be modied so that this capability is no longer reported with ordinary sound cards. This will break applications requiring it.
Please take a look at the Audio timing considerations section for more information about audio timing and latency issues.
Audio device capabilities like PCM_CAP_REALTIME can be checked using the SNDCTL_AUDIOINFO or SNDCTL_DSP_GETCAPS ioctl calls.