# Sequences, Screens, Layers and Clips
Many different structures are used to organize media, cues, effects, etc. on the Timeline. Make sure you have a good understanding of what these structures do and how they are used. The following sections of the documentation (from here to Scroll and Pan on the Timeline) provide information on how Sequences, Screens, Layers and Clips are used.
## Sequences
A Sequence contains all of the Screens, Layers and Clips used in a project, and it provides a representation of the Show’s temporal structure. This is where you will organize and edit media, cues, effects, etc.
A project can have multiple Sequences, but you can only render one Sequence at a time (i.e. the Sequence that is currently selected). Additional Sequences can be used as editing bins to build specific segments of a Show or to hold alternative versions of it.
### 
### Select a Sequence
To select a Sequence:
* **`Click`** on a **Sequence tab** to activate a specific Sequence and access its content.
### Create a Sequence
There are three ways to create a new Sequence:
* Click on the **`+`** button located to the right of the Sequence tabs; or
* Press **`Ctrl`**+**`T`** with the Timeline module in focus; or
* Select **{File > Add sequence}** from the Timeline menu bar.
### Delete a Sequence
To delete a Sequence:
1. **`Right-click`** on the tab linked to the Sequence you want to delete. This will give you access to its contextual menu.
2. Select **{Delete}** from the contextual menu.
## Screens
Any 3D object that was created or imported in the 3D Scene will become a Screen (with the notable exception of Decorative Objects). Screens are virtual structures that represent real-world projection screens. A Screen will coexist in the 3D Scene module (where it is created, then calibrated) and in the Timeline module. Each Screen has its own section of the Timeline, where you can create all of the Layers it will hold.
### Create Screens
Screens are not created in the Timeline module per se. When a 3D object is added in the 3D Scene, TACHYON will automatically recognize it as a Screen. A newly created Screen will add its own section to the Timeline.
### Collapse and Expand Screens
In order to collapse or expand a Screen **`click`** on the small triangle located beside the Screen’s name.
### Add Screen Metadata
It is possible to add text metadata to a Screen by accessing the Screen Properties (see Clip Properties in Programming a Show). The metadata attached to a Screen can be used to show or hide specific Screens when executing a search command.
> **Example:** if you add text metadata such as “Aisle Screens” to some of the Screens as a way to identify them, you can easily find them when performing a search.
### Screen Render Resolution
Screens have a render resolution. The render resolution represents the amount of pixels used to display images on a Screen. You can set a Screen’s render resolution by adjusting its width and height parameters in the Screen Properties (see Clip Properties in Programming a Show).
{% hint style="info" %}
When determining a Screen’s resolution many different factors need to be taken into account:
* the Screen’s physical size
* its ratio
* the distance between its position and the audience
* the resolution of the media that will be displayed on it.
{% hint style="success" %}
The best practice when choosing resolution is to match the ratio of the Screen and the resolution of the media that will be displayed on it.
Insufficient resolution will result in a pixelated image. Using a higher resolution than the media being displayed is a waste of computing resources.
{% endhint %}
{% endhint %}
### Search for a Screen
A search box is located at the top of the Layers list. You can enter text in the box to filter out some of the Screens on the list.
Screens that remain visible in the Layers list will be the ones that match the name or metadata tag entered into the search box.
{% hint style="info" %}
Note that the names of the 3D objects from which the Screens originate are taken into account by the search box filter.
{% endhint %}
### The Root
The Root can be thought of as an invisible Screen that holds various Clip types (see Section Clip Types in Programming a Show). These Clips are independent from any of the actual Screens created in the 3D Scene.
{% hint style="info" %}
Clips placed in the Root can be referenced by other Clips (such as Proxy Clips, Stack FX Clips,Virtual Projectors, etc.).
{% endhint %}
{% hint style="success" %}
It is considered a best practice to **place Cue Clips in the Root** because by doing this, they will appear at the top of all of the other Screens. Also, since the search box filter affects the visibility of the Screens but not the Root, Cues placed in the Root will always be visible.
{% endhint %}
## Layers
Layers are represented as **horizontal tracks in the Timeline**. They can store many Clips horizontally. Layers can be stacked up vertically to create composited scenes. Layers are also useful when **building real-time effects** by combining multiple FX Stack Clips. They are also useful in contexts where automation relies on Cue Clips.
{% hint style="info" %}
TACHYON’s Layers can hold many clips.
{% endhint %}
### Create New Layers
To create a new Layer:
1. Select one of the Screens (or the Root) by clicking on its entry in the Layers list;
2. Click on the **`+`** button located in the Master Layer panel.
The new Layer will be added at the bottom of the Layers list.
By pressing **`Ctrl`**+**`＋`** the new Layer will be inserted directly below the Layer that is currently selected.
{% hint style="info" %}
A newly created Layer might not be immediately visible. You have to **`Double-click`** on the Screen or on the triangle found next to the Screen’s name in order to reveal the Layers stored inside it.
{% endhint %}
### Reorganize the Layer Order
All Layers can be manipulated with the mouse in order to change their position in the Layers list:
* **`Click`+Drag+Drop** any Layer to where you want it.
Layers can also be dragged from one Screen to another using the same method.
### Layer Rendering Order
In TACHYON, the rendering order is organized sequentially, from top to bottom. This means **the lowest item in the list will always be the last one rendered**, and as a result it will be placed on top of the composition. This design applies to both the Timeline module (where compositing is done) and the 3D Scene list.
It is important to remember that the logic of TACHYON’s rendering order is the inverse of Adobe’s image compositing software.
## Clips
A Clip is a container that can hold various time-based components such as media, cues, effects, etc. (see Clip Types in Programming a Show for a complete list of the Clip types and their description).
Clips are placed within Layers (which in turn are placed in Screens, or in the Root). Stacking Clips vertically in the Layers belonging to the same Screen (or in the Root) will allow the creation of visual compositions through Layer blending (see Blending – Create Compositions in Programming a Show).
Clips have a **fixed duration defined by their borders**.
{% hint style="info" %}
By default, the duration of the newly created Clip will match the duration of the whole project.
{% endhint %}
The Clip’s default duration can be changed by entering a new temporal value for Clips in the field located in the Timeline Default values window. To access the Timeline Default values window **`click`** on the **General tab** in the **Settings module**.
### Add Clips
* **`Right-click`** on any track on the Timeline (each Layer has a its own track) to open a contextual menu that contains the following options for adding new Clips (or use the dedicated shortcuts in the Timeline module):
* Add Empty Clip **`Ctrl`****+****`N`**
* Add Media Clip (Image, Video, Sound) **`Ctrl`****+****`M`**
* Add FX Stack Clip **`Ctrl`****+****`E`**
* Add Virtual Projector Clip **`Ctrl`****+****`R`**
* Add Input Device Clip **`Ctrl`****+****`I`**
* Add Cue Clip **`Ctrl`****+****`U`**
* Add Proxy Clip **`Ctrl`****+****`P`**
* **Drag+Drop** a media file from the **File Manager** module onto a track to create a n**ew Media Clip**.
* **Drag+Drop** a cue from the **Cue Editor** module onto a track to create a **new Cue Clip**.
* **Drag+Drop** a Live input from the **I/O Manager** module onto a track to create a **new Live Input Clip**.
### Select a Single Clip
* **`Click`** on a Clip to select it.
### Select Multiple Clips
* **`Ctrl`****+`Click`** on Clips
OR
* Draw a selection square across the Layers to perform a group selection. (This only works if you draw the selection square within the tracks that are identified by the lighter grey area.)
{% hint style="info" %}
The selection square works across Screens.
{% endhint %}
### Delete Clips
1. Select the Clips you want to delete and press the **`Delete`** key. A Confirmation Box will open to make sure you really want to delete the Clip.
2. Click on the **`Delete`** key to delete the Clip.
### Change Clip Type
Clip capacities (media playback, send a cue, etc.) are defined by their type (media, cue, effect, etc.). A Clip type is selected whenever a Clip is created.
You can also change a Clip type later on without affecting its duration or location in the Timeline by doing the following:
* Select the Clip and then select an option from the Clip Type dropdown menu located in the Shared Clip Properties window section of the Timeline module.
{% hint style="warning" %}
The Clip type cannot be changed when multiple Clips are selected.
{% endhint %}
### Change Clip Colors
1. **`Right-click`** on a Clip (or a group of multi-selected Clips).
2. Select **{Change color}** from the contextual menu. A color picker pop-up window will open.
3. Choose the desired color and close the color picker.
### Reset Clip Colors
1. **`Right-click`** on a Clip (or a group of multi-selected Clips).
2. Select **{Reset color}** from the contextual menu. The selected Clips will reset their color to the default specified in the Settings module.
**Change a Clip Type Color**
1. Press **`Alt`****+****`S`** or select **{System > Settings}** to open the Settings module.
2. **`Click`** on the **General tab** to access the Default Clip Colors list.
3. **`Click`** on any of the Clip type buttons in the list to open a **color picker pop-up window**.
4. Choose the desired color and close the color picker.