AudioSampleProvider

Description

Provides access to the audio samples generated by Unity objects such as VideoPlayer.

This class is meant to be usable outside the main thread and the implementation assumes a single consumer at a time invoking AudioSampleProvider.ConsumeSampleFrames. Audio data can be accessed both from C# and from C++, depending on what has to be done with this data.

The following is an example of how to access samples from C# using an accessor obtained from the VideoPlayer:

using UnityEngine;
using Unity.Collections;
using UnityEngine.Experimental.Video;
using UnityEngine.Experimental.Audio;
using UnityEngine.Video;

public class ManagedAudioOutput : MonoBehaviour
{
    AudioSampleProvider provider;

    void Start()
    {
        VideoPlayer vp = GetComponent<VideoPlayer>();
        vp.audioOutputMode = VideoAudioOutputMode.APIOnly;
        vp.prepareCompleted += Prepared;
        vp.Prepare();
    }

    void Prepared(VideoPlayer vp)
    {
        provider = vp.GetAudioSampleProvider(0);
        provider.sampleFramesAvailable += SampleFramesAvailable;
        provider.enableSampleFramesAvailableEvents = true;
        provider.freeSampleFrameCountLowThreshold = provider.maxSampleFrameCount / 4;
        vp.Play();
    }

    void SampleFramesAvailable(AudioSampleProvider provider, uint sampleFrameCount)
    {
        using (NativeArray<float> buffer = new NativeArray<float>(
                       (int)sampleFrameCount * provider.channelCount, Allocator.Temp))
        {
            var sfCount = provider.ConsumeSampleFrames(buffer);
            Debug.LogFormat("SetupSoftwareAudioOut.Available got {0} sample frames.", sfCount);
            // Do something with the samples here...
        }
    }
}

The following is an example of how to access samples from C++. The setup has to be done in C# and then Unity's core and the native plug-in can call into each other without having to go through managed code.

using System;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.Experimental.Video;
using UnityEngine.Experimental.Audio;
using UnityEngine.Video;

public class NativeAudioOutput : MonoBehaviour
{
    AudioSampleProvider provider;
    AudioSampleProvider.SampleFramesEventNativeFunction sampleFramesAvailableNativeHandler =
        SampleFramesAvailable;

    void Start()
    {
        VideoPlayer vp = GetComponent<VideoPlayer>();
        vp.audioOutputMode = VideoAudioOutputMode.APIOnly;
        vp.prepareCompleted += Prepared;
        vp.Prepare();
    }

    void Prepared(VideoPlayer vp)
    {
        provider = vp.GetAudioSampleProvider(0);
        provider.freeSampleFrameCountLowThreshold = provider.maxSampleFrameCount - 1024;

        SetConsumeSampleFramesFunction(
            AudioSampleProvider.consumeSampleFramesNativeFunction, provider.id,
            provider.channelCount, provider.sampleRate);
        provider.SetSampleFramesAvailableNativeHandler(
            sampleFramesAvailableNativeHandler, (IntPtr)0);

        vp.Play();
    }

    private const string pluginName =
#if UNITY_IPHONE
        "__Internal"
#else
        "NativeAudioOutputPlugin"
#endif
    ;

    [DllImport(pluginName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
    private static extern void SetConsumeSampleFramesFunction(
        AudioSampleProvider.ConsumeSampleFramesNativeFunction cb, uint id, ushort channelCount, uint sampleRate);

    [AOT.MonoPInvokeCallback(typeof(AudioSampleProvider.SampleFramesEventNativeFunction))]
    [DllImport(pluginName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
    private static extern void SampleFramesAvailable(IntPtr userData, uint id, uint sampleFrameCount);
}

And here is the accompanying C++ plug-in:

#include <algorithm>
#include <stdint.h>

typedef uint32_t(__cdecl *ConsumeSampleFramesFunction)(
    uint32_t providerId, float* interleavedSampleFrames, uint32_t sampleFrameCount);

ConsumeSampleFramesFunction ConsumeSampleFrames = NULL;
uint32_t providerId = -1;
float* buffer = NULL;
uint32_t bufferSampleFrameCount = 0;
uint32_t availableSampleFrameCount = 0;

extern "C" __cdecl void SetConsumeSampleFramesFunction(
    ConsumeSampleFramesFunction function, uint32_t id, uint16_t channelCount, uint32_t sampleRate)
{
    ConsumeSampleFrames = function;
    providerId = id;
    delete[] buffer;
    buffer = new float[channelCount * sampleRate]; // 1s worth of sample frames.
    bufferSampleFrameCount = sampleRate;
}

extern "C" __cdecl void SampleFramesAvailable(void* userData, uint32_t id, uint32_t sampleFrameCount)
{
    if (ConsumeSampleFrames == NULL)
        return;

    // We consume the sample frames from the handler that tells us that there are some available.
    // But we could also invoke this regularly from another thread, for example the thread providing
    // samples to an audio device.
    const uint32_t consumedSampleFrameCount = ConsumeSampleFrames(
            providerId, buffer, std::min(bufferSampleFrameCount, sampleFrameCount));
    // Do something with the samples here...
}

Static Properties

Properties

Public Methods

Events

Delegates