_bindAction( action, prototypeAction ) {

		const root = action._localRoot || this._root,
			tracks = action._clip.tracks,
			nTracks = tracks.length,
			bindings = action._propertyBindings,
			interpolants = action._interpolants,
			rootUuid = root.uuid,
			bindingsByRoot = this._bindingsByRootAndName;

		let bindingsByName = bindingsByRoot[ rootUuid ];

		if ( bindingsByName === undefined ) {

			bindingsByName = {};
			bindingsByRoot[ rootUuid ] = bindingsByName;

		}

		for ( let i = 0; i !== nTracks; ++ i ) {

			const track = tracks[ i ],
				trackName = track.name;

			let binding = bindingsByName[ trackName ];

			if ( binding !== undefined ) {

				++ binding.referenceCount;
				bindings[ i ] = binding;

			} else {

				binding = bindings[ i ];

				if ( binding !== undefined ) {

					// existing binding, make sure the cache knows

					if ( binding._cacheIndex === null ) {

						++ binding.referenceCount;
						this._addInactiveBinding( binding, rootUuid, trackName );

					}

					continue;

				}

				const path = prototypeAction && prototypeAction.
					_propertyBindings[ i ].binding.parsedPath;

				binding = new PropertyMixer(
					PropertyBinding.create( root, trackName, path ),
					track.ValueTypeName, track.getValueSize() );

				++ binding.referenceCount;
				this._addInactiveBinding( binding, rootUuid, trackName );

				bindings[ i ] = binding;

			}

			interpolants[ i ].resultBuffer = binding.buffer;

		}

	}
A scaling factor for the global time.

Note: Setting this member to `0` and later back to `1` is a
possibility to pause/unpause all actions that are controlled by this
mixer.

@type {number}
@default 1