Can't record with Unity Recorder

Unity
9

Thanks for sharing, with a few modifications to your code i finally got the result. Put this script somewhere in a root or a start scene, fmod audio will be captured into audio source, but only when Unity Recorder is on (Time.captureFramerate != 0).
But you need to toggle “Allow unsafe” in the Player settings for this to be compiled, or use jeff_fmod’s version of fmod read dsp callback, those changes are just for some performance to avoid array allocations.

using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using FMOD;
using FMODUnity;
using UnityEngine;
using Debug = UnityEngine.Debug;

namespace Recorder
{
    
    [RequireComponent(typeof(AudioSource))]
    public sealed class FmodRecorderHelper : MonoBehaviour
    {
        private readonly List<float> _buffer = new();
        private DSP_DESCRIPTION _dspDesc;
        private DSP _dsp;
        private bool _isRunning = false;
        private bool _isCreatedDsp = false;

        private static bool _isInitialized = false;
        
        private void Awake()
        {
            if (_isInitialized)
            {
                Destroy(this);
                return;
            }
            
            _isInitialized = true;
            DontDestroyOnLoad(this);
        }

        private void Reset()
        {
            var audioSource = GetComponent<AudioSource>();

            audioSource.spatialBlend = 0f;
            audioSource.reverbZoneMix = 0f;
        }

        private void OnDestroy()
        {
            RemoveDsp();
        }

        private void OnAudioFilterRead(float[] data, int channels)
        {
            if (!_isRunning) return;

            if (_buffer.Count >= data.Length)
            {
                // Copy from intermediate buffer into Unity's audio buffer
                for (int i = 0; i < data.Length; i++)
                {
                    data[i] = _buffer[i];
                }
                
                _buffer.RemoveRange(0, data.Length);
            }
        }

        private void Update()
        {
            if (Time.captureFramerate == 0)
            {
                if (_isRunning) RemoveDsp();
                return;
            }
            
            if (_isRunning) return;
            
            CreateDsp();
            
            RuntimeManager.CoreSystem.getMasterChannelGroup(out var group);
            if (group.hasHandle())
            {
                _isRunning = true;
                CHECK_RESULT(group.addDSP(0, _dsp));
            } 
        }

        private void CreateDsp()
        {
            if (_isCreatedDsp) return;
            _isCreatedDsp = true;
            
            _dspDesc = new DSP_DESCRIPTION
            {
                numinputbuffers = 1,
                numoutputbuffers = 1,
                read = (ref DSP_STATE dsp_state, IntPtr inbuffer, IntPtr outbuffer, uint length, int inchannels, ref int outchannels) =>
                {
                    if (length > 0)
                    {
                        unsafe
                        {
                            // Copy to buffer
                            var tmp = new Span<float>(inbuffer.ToPointer(), (int) length * inchannels);
                            for (int i = 0; i < tmp.Length; i++)
                            {
                                _buffer.Add(tmp[i]);
                            }
                            
                            // Silence FMOD output
                            tmp = new Span<float>(outbuffer.ToPointer(), (int) length * inchannels);
                            for (int i = 0; i < tmp.Length; i++)
                            {
                                tmp[i] = 0f;
                            }
                        }
                    }

                    return RESULT.OK;
                },
            };

            var result = RuntimeManager.CoreSystem.createDSP(ref _dspDesc, out _dsp);

            var unitySpeakerMode = AudioSettings.GetConfiguration().speakerMode; 
            var speakerMode = unitySpeakerMode switch
            {
                AudioSpeakerMode.Mono => SPEAKERMODE.MONO,
                AudioSpeakerMode.Stereo => SPEAKERMODE.STEREO,
                AudioSpeakerMode.Quad => SPEAKERMODE.QUAD,
                AudioSpeakerMode.Surround => SPEAKERMODE.SURROUND,
                AudioSpeakerMode.Mode5point1 => SPEAKERMODE._5POINT1,
                AudioSpeakerMode.Mode7point1 => SPEAKERMODE._7POINT1,
                AudioSpeakerMode.Prologic => SPEAKERMODE.DEFAULT,
                _ => SPEAKERMODE.DEFAULT,
            };

            int numChannels = unitySpeakerMode switch
            {
                AudioSpeakerMode.Mono => 1,
                AudioSpeakerMode.Stereo => 2,
                AudioSpeakerMode.Quad => 4,
                AudioSpeakerMode.Surround => 5,
                AudioSpeakerMode.Mode5point1 => 6,
                AudioSpeakerMode.Mode7point1 => 7,
                AudioSpeakerMode.Prologic => 2,
                _ => 2,
            }; 
            
            _dsp.setChannelFormat(CHANNELMASK.STEREO, numChannels, speakerMode);
            
            CHECK_RESULT(result);
        }

        private void RemoveDsp()
        {
            _isRunning = false;
            
            if (!_isCreatedDsp) return;
            _isCreatedDsp = false;
            
            CHECK_RESULT(RuntimeManager.CoreSystem.getMasterChannelGroup(out var group));
            CHECK_RESULT(group.removeDSP(_dsp));
            CHECK_RESULT(_dsp.release());
        }
        
        private static void CHECK_RESULT(RESULT result, [CallerLineNumber] int sourceLineNumber = 0)
        {
            if (result == RESULT.OK) return;
            Debug.LogError($"Call to FMOD API failed with result: \"{Error.String(result)}\" line: {sourceLineNumber}");
        }
    }
    
}