Data Formats
All the system sAPOs are designed to process float32 pulse code modulation (PCM) data. To prevent unnecessary format conversions, LFX and GFX sAPOs should process data in float32 PCM format. A typical GFX for an int16 PCM endpoint uses the float32 PCM format for both input and output. The graph builder attaches a system-provided float32-int16 converter to the endpoint-facing side of the sAPO to convert the audio stream to or from int16 PCM format. GFX sAPOs can omit the system-supplied format converter and process data in the native device format. However, the audio engine-facing side of the GFX must still support the float32 PCM format.
GFX sAPOs can support an encoded output format such as AC3 that can handle multiple speaker configurations. In that case, the sAPO should get the speaker configuration information from the endpoint property store. It can then return S_FALSE to suggest an input (mix) format when IsInputFormatSupported is called with the encoded format as opposite. The GFX sAPO should return a float format that has the sample rate and speaker configuration of the “decoded” format.
Note: An sAPO can suggest an audio format only during calls to IsInputFormatSupported or IsOutputFormatSupported.
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