Add example Unity Project

Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/Audio/AudioClipProperties.cs

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+using System;
+using UnityEngine.Playables;
+
+namespace UnityEngine.Timeline
+{
+    [Serializable]
+    [NotKeyable]
+    class AudioClipProperties : PlayableBehaviour
+    {
+        [Range(0.0f, 1.0f)]
+        public float volume = 1.0f;
+    }
+}

Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/Audio/AudioClipProperties.cs.meta

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Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/Audio/AudioMixerProperties.cs

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+using System;
+using UnityEngine.Audio;
+using UnityEngine.Playables;
+
+namespace UnityEngine.Timeline
+{
+    [Serializable]
+    class AudioMixerProperties : PlayableBehaviour
+    {
+        [Range(0.0f, 1.0f)]
+        public float volume = 1.0f;
+
+        [Range(-1.0f, 1.0f)]
+        public float stereoPan = 0.0f;
+
+        [Range(0.0f, 1.0f)]
+        public float spatialBlend = 0.0f;
+
+        public override void PrepareFrame(Playable playable, FrameData info)
+        {
+            if (!playable.IsValid() || !playable.IsPlayableOfType<AudioMixerPlayable>())
+                return;
+
+            var inputCount = playable.GetInputCount();
+
+            for (int i = 0; i < inputCount; ++i)
+            {
+                if (playable.GetInputWeight(i) > 0.0f)
+                {
+                    var input = playable.GetInput(i);
+
+                    if (input.IsValid() && input.IsPlayableOfType<AudioClipPlayable>())
+                    {
+                        var audioClipPlayable = (AudioClipPlayable)input;
+                        var audioClipProperties = input.GetHandle().GetObject<AudioClipProperties>();
+
+                        audioClipPlayable.SetVolume(Mathf.Clamp01(volume * audioClipProperties.volume));
+                        audioClipPlayable.SetStereoPan(Mathf.Clamp(stereoPan, -1.0f, 1.0f));
+                        audioClipPlayable.SetSpatialBlend(Mathf.Clamp01(spatialBlend));
+                    }
+                }
+            }
+        }
+    }
+}

Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/Audio/AudioMixerProperties.cs.meta

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Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/Audio/AudioPlayableAsset.cs

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+using System;
+using System.Collections.Generic;
+using UnityEngine.Audio;
+#if UNITY_EDITOR
+using System.ComponentModel;
+#endif
+using UnityEngine.Playables;
+
+namespace UnityEngine.Timeline
+{
+    /// <summary>
+    /// PlayableAsset wrapper for an AudioClip in Timeline.
+    /// </summary>
+    [Serializable]
+#if UNITY_EDITOR
+    [DisplayName("Audio Clip")]
+#endif
+    public class AudioPlayableAsset : PlayableAsset, ITimelineClipAsset
+    {
+        [SerializeField] AudioClip m_Clip;
+#pragma warning disable 649 //Field is never assigned to and will always have its default value
+        [SerializeField] bool m_Loop;
+        [SerializeField, HideInInspector] float m_bufferingTime = 0.1f;
+        [SerializeField] AudioClipProperties m_ClipProperties = new AudioClipProperties();
+
+        // the amount of time to give the clip to load prior to it's start time
+        internal float bufferingTime
+        {
+            get { return m_bufferingTime;  }
+            set { m_bufferingTime = value; }
+        }
+
+#if UNITY_EDITOR
+        Playable m_LiveClipPlayable = Playable.Null;
+
+#endif
+
+        /// <summary>
+        /// The audio clip to be played
+        /// </summary>
+        public AudioClip clip
+        {
+            get { return m_Clip; }
+            set { m_Clip = value; }
+        }
+
+        /// <summary>
+        /// Whether the audio clip loops.
+        /// </summary>
+        /// <remarks>
+        /// Use this to loop the audio clip when the duration of the timeline clip exceeds that of the audio clip.
+        /// </remarks>
+        public bool loop
+        {
+            get { return m_Loop; }
+            set { m_Loop = value; }
+        }
+
+        /// <summary>
+        /// Returns the duration required to play the audio clip exactly once
+        /// </summary>
+        public override double duration
+        {
+            get
+            {
+                if (m_Clip == null)
+                    return base.duration;
+
+                // use this instead of length to avoid rounding precision errors,
+                return (double)m_Clip.samples / m_Clip.frequency;
+            }
+        }
+
+        /// <summary>
+        /// Returns a description of the PlayableOutputs that may be created for this asset.
+        /// </summary>
+        public override IEnumerable<PlayableBinding> outputs
+        {
+            get { yield return AudioPlayableBinding.Create(name, this); }
+        }
+
+        /// <summary>
+        /// Creates the root of a Playable subgraph to play the audio clip.
+        /// </summary>
+        /// <param name="graph">PlayableGraph that will own the playable</param>
+        /// <param name="go">The GameObject that triggered the graph build</param>
+        /// <returns>The root playable of the subgraph</returns>
+        public override Playable CreatePlayable(PlayableGraph graph, GameObject go)
+        {
+            if (m_Clip == null)
+                return Playable.Null;
+
+            var audioClipPlayable = AudioClipPlayable.Create(graph, m_Clip, m_Loop);
+            audioClipPlayable.GetHandle().SetScriptInstance(m_ClipProperties.Clone());
+
+#if UNITY_EDITOR
+            m_LiveClipPlayable = audioClipPlayable;
+#endif
+
+            return audioClipPlayable;
+        }
+
+        /// <summary>
+        /// Returns the capabilities of TimelineClips that contain an AudioPlayableAsset
+        /// </summary>
+        public ClipCaps clipCaps
+        {
+            get
+            {
+                return ClipCaps.ClipIn |
+                    ClipCaps.SpeedMultiplier |
+                    ClipCaps.Blending |
+                    (m_Loop ? ClipCaps.Looping : ClipCaps.None);
+            }
+        }
+
+#if UNITY_EDITOR
+        internal void LiveLink()
+        {
+            if (!m_LiveClipPlayable.IsValid())
+                return;
+
+            var audioMixerProperties = m_LiveClipPlayable.GetHandle().GetObject<AudioClipProperties>();
+
+            if (audioMixerProperties == null)
+                return;
+
+            audioMixerProperties.volume = m_ClipProperties.volume;
+        }
+
+#endif
+    }
+}

Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/Audio/AudioPlayableAsset.cs.meta

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Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/Audio/AudioTrack.cs

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+using System;
+using System.Collections.Generic;
+using UnityEngine.Audio;
+using UnityEngine.Playables;
+
+namespace UnityEngine.Timeline
+{
+    /// <summary>
+    /// A Timeline track that can play AudioClips.
+    /// </summary>
+    [Serializable]
+    [TrackClipType(typeof(AudioPlayableAsset), false)]
+    [TrackBindingType(typeof(AudioSource))]
+    [ExcludeFromPreset]
+    public class AudioTrack : TrackAsset
+    {
+        [SerializeField]
+        AudioMixerProperties m_TrackProperties = new AudioMixerProperties();
+
+#if UNITY_EDITOR
+        Playable m_LiveMixerPlayable = Playable.Null;
+
+#endif
+
+        /// <summary>
+        /// Create an TimelineClip for playing an AudioClip on this track.
+        /// </summary>
+        /// <param name="clip">The audio clip to play</param>
+        /// <returns>A TimelineClip with an AudioPlayableAsset asset.</returns>
+        public TimelineClip CreateClip(AudioClip clip)
+        {
+            if (clip == null)
+                return null;
+
+            var newClip = CreateDefaultClip();
+
+            var audioAsset = newClip.asset as AudioPlayableAsset;
+            if (audioAsset != null)
+                audioAsset.clip = clip;
+
+            newClip.duration = clip.length;
+            newClip.displayName = clip.name;
+
+            return newClip;
+        }
+
+        internal override Playable CompileClips(PlayableGraph graph, GameObject go, IList<TimelineClip> timelineClips, IntervalTree<RuntimeElement> tree)
+        {
+            var clipBlender = AudioMixerPlayable.Create(graph, timelineClips.Count);
+
+#if UNITY_EDITOR
+            clipBlender.GetHandle().SetScriptInstance(m_TrackProperties.Clone());
+            m_LiveMixerPlayable = clipBlender;
+#else
+            if (hasCurves)
+                clipBlender.GetHandle().SetScriptInstance(m_TrackProperties.Clone());
+#endif
+
+            for (int i = 0; i < timelineClips.Count; i++)
+            {
+                var c = timelineClips[i];
+                var asset = c.asset as PlayableAsset;
+                if (asset == null)
+                    continue;
+
+                var buffer = 0.1f;
+                var audioAsset = c.asset as AudioPlayableAsset;
+                if (audioAsset != null)
+                    buffer = audioAsset.bufferingTime;
+
+                var source = asset.CreatePlayable(graph, go);
+                if (!source.IsValid())
+                    continue;
+
+                if (source.IsPlayableOfType<AudioClipPlayable>())
+                {
+                    // Enforce initial values on all clips
+                    var audioClipPlayable = (AudioClipPlayable)source;
+                    var audioClipProperties = audioClipPlayable.GetHandle().GetObject<AudioClipProperties>();
+
+                    audioClipPlayable.SetVolume(Mathf.Clamp01(m_TrackProperties.volume * audioClipProperties.volume));
+                    audioClipPlayable.SetStereoPan(Mathf.Clamp(m_TrackProperties.stereoPan, -1.0f, 1.0f));
+                    audioClipPlayable.SetSpatialBlend(Mathf.Clamp01(m_TrackProperties.spatialBlend));
+                }
+
+                tree.Add(new ScheduleRuntimeClip(c, source, clipBlender, buffer));
+                graph.Connect(source, 0, clipBlender, i);
+                source.SetSpeed(c.timeScale);
+                source.SetDuration(c.extrapolatedDuration);
+                clipBlender.SetInputWeight(source, 1.0f);
+            }
+
+            ConfigureTrackAnimation(tree, go, clipBlender);
+
+            return clipBlender;
+        }
+
+        /// <inheritdoc/>
+        public override IEnumerable<PlayableBinding> outputs
+        {
+            get { yield return AudioPlayableBinding.Create(name, this); }
+        }
+
+#if UNITY_EDITOR
+        internal void LiveLink()
+        {
+            if (!m_LiveMixerPlayable.IsValid())
+                return;
+
+            var audioMixerProperties = m_LiveMixerPlayable.GetHandle().GetObject<AudioMixerProperties>();
+
+            if (audioMixerProperties == null)
+                return;
+
+            audioMixerProperties.volume = m_TrackProperties.volume;
+            audioMixerProperties.stereoPan = m_TrackProperties.stereoPan;
+            audioMixerProperties.spatialBlend = m_TrackProperties.spatialBlend;
+        }
+
+#endif
+
+        void OnValidate()
+        {
+            m_TrackProperties.volume = Mathf.Clamp01(m_TrackProperties.volume);
+            m_TrackProperties.stereoPan = Mathf.Clamp(m_TrackProperties.stereoPan, -1.0f, 1.0f);
+            m_TrackProperties.spatialBlend = Mathf.Clamp01(m_TrackProperties.spatialBlend);
+        }
+    }
+}

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