TrackAssetExtension.cs

using System;
using System.Reflection;
using UnityEngine;
using UnityEngine.Playables;
using UnityEngine.Timeline;

public static class TrackAssetExtensions
{
	static Type TrackAssetType = typeof(TrackAsset);
	static Type TimelineClipType = typeof(TimelineClip);

	public static TimelineClip CreateClipInternal(this TrackAsset track)
	{
		var method = TrackAssetType.GetMethod("CreateNewClipContainerInternal", BindingFlags.NonPublic | BindingFlags.Instance);
		return method.Invoke(track, new object[] { }) as TimelineClip;
	}

	public static TimelineClip CreateClipInternal(this TrackAsset track, Type type)
	{
		if (type == null || !typeof(IPlayableAsset).IsAssignableFrom(type) || !typeof(ScriptableObject).IsAssignableFrom(type))
		{
			throw new InvalidOperationException("Cannot create an clip for type " + type.Name);
		}

		var scriptableObject = ScriptableObject.CreateInstance(type);

		if (scriptableObject == null)
		{
			throw new InvalidOperationException("Could not create an instance of the ScriptableObject type " + type.Name);
		}

		scriptableObject.name = type.Name;

		// Creates a valid clip
		var timelineClip = track.CreateClipInternal();

		// Sets the clip title, asset, and length
		var method = TrackAssetType.GetMethod("OnCreateClipFromAsset", BindingFlags.NonPublic | BindingFlags.Instance);
		method.Invoke(track, new object[] { scriptableObject, timelineClip });

		// Add the clip to m_Clips
		track.AddClip(timelineClip);

		return timelineClip;
	}

	public static TimelineClip CreateClipInternal<T>(this TrackAsset track) where T : ScriptableObject, IPlayableAsset, new()
	{
		return track.CreateClipInternal(typeof(T));
	}

	public static TimelineClip CreateClip(this TrackAsset track, Type type)
	{
		var method = TrackAssetType.GetMethod("CreateClipOfType", BindingFlags.NonPublic | BindingFlags.Instance);
		return method.Invoke(track, new object[] { type }) as TimelineClip;
	}

	public static TimelineClip CreateClip<T>(this TrackAsset track) where T : ScriptableObject, IPlayableAsset, new()
	{
		return track.CreateClip(typeof(T));
	}

	public static void AddClip(this TrackAsset track, TimelineClip clip)
	{
		var method = TrackAssetType.GetMethod("AddClip", BindingFlags.NonPublic | BindingFlags.Instance);
		method.Invoke(track, new object[] { clip });
	}

	public static void RemoveClip(this TrackAsset track, TimelineClip clip)
	{
		var method = TrackAssetType.GetMethod("RemoveClip", BindingFlags.NonPublic | BindingFlags.Instance);
		method.Invoke(track, new object[] { clip });
	}
}