Plugins:PepperAudioAPI: Difference between revisions

satisfy scheduling demands. This model assumes the application programmer will setup the dedicated audio thread (and has access to a thread API such as pthreads.)

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Callback Mode: While an application is performing audio output, it will receive callbacks at a regular interval. If an application needs to enter a state where audio output isn't required, it may wish to suppress the callback to save power and/or CPU cycles. The application can suppress the audio callback in two ways: 1) It can shutdown the audio context, and at a later time, when the application needs to resume audio output, it can re-initialize a new audio context. This approach may have long latency. 2) If setStateContext(npp, NPAudioContextStateCallback, NPAudioCallbackStop) is invoked on the NPAPI thread, callbacks will be suspended and the implicit audio thread will go into a sleep state. To resume audio playback and callbacks, the NPAPI thread should invoke setStateContext(npp,NPAudioContextStateCallback, NPAudioCallbackStop), which will resume callbacks in a low latency time frame.

Push Mode: In the blocking push model, flushContext() will block (sleep) until the audio context is ready to consume another chunk of sample data. If the audio thread does not call flushContext() within a short period of time (the duration of which depends on the sample frame count and sample frequency), the audio context will automatically emit silence. Normally, an audio thread will continuously make calls to the blocking flushContext() call to emit long continuous periods of audio output. If the application enters a state where no audio output is needed for an extended duration and it wishes to reduce CPU load, the application has one of two options. 1) Shutdown the audio context and exit the audio thread. When audio playback needs to resume, it can re-spawn the audio thread and re-initialize an audio context. This approach may have a long latency. 2) The application can sleep the audio thread during long periods of silence by waiting on a pthread cond_var. When the main thread is ready to resume audio playback, it can signal the condition variable to wake up the sleeping audio thread. This approach is expected to resume audio output in a low latency time frame.

The basic Pepper API consists of: queryCapability, queryConfig, initializeContext, setStateContext, getStateContext, flushContext, and destroyContext.

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This section goes into more detail on what queryCapability() returns based on the input