Apply custom voice effects with real-time audio manipulation

// An app-defined function that takes a microphone buffer and generates a new
// buffer that should be transmitted to other chat controls.
std::vector<uint8_t>
ProcessLocalVoiceBuffer(
    PartyMutableDataBuffer* inputBuffer
    );

void
ProcessLocalMicrophoneAudioForSingleChatControl(
    PartyLocalChatControl* chatControl
    )
{
    // Get the voice stream from which we want to retrieve audio. This provides
    // the audio generated by the chat control's input device.
    PartyAudioManipulationSourceStream* voiceStream;
    RETURN_VOID_IF_FAILED(chatControl->GetAudioManipulationVoiceStream(&voiceStream));

    // Get the capture stream to which we want to submit audio. This is used to
    // submit audio that will be transmitted to other chat controls.
    PartyAudioManipulationSinkStream* captureStream;
    RETURN_VOID_IF_FAILED(chatControl->GetAudioManipulationCaptureStream(&captureStream));

    // Get the next audio buffer from the voice stream.
    PartyMutableDataBuffer buffer;
    RETURN_VOID_IF_FAILED(voiceStream->GetNextBuffer(&buffer));

    // If we retrieved a buffer, process it.
    if (buffer.bufferByteCount > 0)
    {
        // Use the buffer we retrieved to generate a new buffer that will be
        // treated as the "real" capture input and transmitted to other chat
        // controls.
        std::vector<uint8_t> processedBuffer = ProcessLocalVoiceBuffer(&buffer);

        // Convert the buffer to a Party type.
        PartyDataBuffer partyBuffer;
        partyBuffer.bufferByteCount = static_cast<uint32_t>(processedBuffer.size());
        partyBuffer.buffer = processedBuffer.data();

        // Submit the processed buffer to the capture stream.
        PartyError error = captureStream->SubmitBuffer(&partyBuffer);
        if (PARTY_FAILED(error))
        {
            printf("Failed to submit buffer to sink stream! error = 0x%08x", error);
        }

        // Return the original buffer back to the voice stream.
        error = voiceStream->ReturnBuffer(buffer.buffer);
        if (PARTY_FAILED(error))
        {
            printf("Failed to return buffer to source stream! error = 0x%08x", error);
        }
    }
}

// This is an app-defined function that takes a local chat control and list of remote voice buffers and generates
// a single mixed buffer to submit to the local chat control's audio output.
std::vector<uint8_t>
GetOutputMixBuffer(
    PartyLocalChatControl& localChatControl,
    const std::map<PartyAudioManipulationSourceStream*, PartyMutableDataBuffer>& remoteVoiceBuffers
    );

void
ProcessRemoteVoiceAudio(
    const std::vector<PartyChatControl*>& remoteChatControls,
    const std::vector<PartyLocalChatControl*>& localChatControls
    )
{
    std::map<PartyAudioManipulationSourceStream*, PartyMutableDataBuffer> remoteVoiceBuffers;

    // Acquire voice buffers from each remote chat control.
    for (auto remoteChatControl : remoteChatControls)
    {
        // Get the voice stream for this chat control from which we will retrieve audio.
        PartyAudioManipulationSourceStream* voiceStream;
        PartyError error = remoteChatControl->GetAudioManipulationVoiceStream(&voiceStream);
        if (PARTY_FAILED(error))
        {
            printf("Failed to get voice stream! error = 0x%08x", error);
            continue;
        }

        // Get the next audio buffer from the voice stream.
        PartyMutableDataBuffer buffer;
        error = voiceStream->GetNextBuffer(&buffer);
        if (PARTY_FAILED(error))
        {
            printf("Failed to get next buffer! error = 0x%08x", error);
            continue;
        }

        // If we retrieved a buffer, cache it in the map for mixing.
        if (buffer.bufferByteCount > 0)
        {
            remoteVoiceBuffers[voiceStream] = buffer;
        }
    }

    // If we didn't acquire any source buffers, we don't have anything to mix.
    if (remoteVoiceBuffers.empty())
    {
        return;
    }

    // Mix the voice buffers and submit to each render stream.
    for (auto localChatControl : localChatControls)
    {
        // Get the render stream for this chat control to which we will submit audio.
        PartyAudioManipulationSinkStream* renderStream;
        PartyError error = localChatControl->GetAudioManipulationRenderStream(&renderStream);
        if (PARTY_FAILED(error))
        {
            printf("Failed to get render stream! error = 0x%08x", error);
            continue;
        }

        // Mix the buffers the buffers to generate a new, mixed buffer.
        std::vector<uint8_t> mixedBuffer = GetOutputMixBuffer(*localChatControl, remoteVoiceBuffers);

        // Convert the buffer to a party type.
        PartyDataBuffer partyBuffer;
        partyBuffer.bufferByteCount = static_cast<uint32_t>(mixedBuffer.size());
        partyBuffer.buffer = mixedBuffer.data();

        // Submit the mixed buffer to the render stream.
        error = renderStream->SubmitBuffer(&partyBuffer);
        if (PARTY_FAILED(error))
        {
            printf("Failed to submit buffer to render stream! error = 0x%08x", error);
        }
    }

    // Release the voice buffers.
    for (auto voiceBuffer : remoteVoiceBuffers)
    {
        // Return the voice buffer that we had cached from this voice stream.
        PartyError error = voiceBuffer.first->ReturnBuffer(voiceBuffer.second.buffer);
        if (PARTY_FAILED(error))
        {
            printf("Failed to return buffer! error = 0x%08x", error);
        }
    }
}