> For the complete documentation index, see [llms.txt](https://docs.lightact.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lightact.com/timelines/syncing-to-a-timecode.md).

# Syncing to a timecode

To sync LightAct to an external timecode the process is as follows:

1. **Receive external TC**: LightAct can receive LTC through Audio input nodes, MTC through MIDI Receiver nodes (both in the Devices window) and Art-Net timecode through DMX In window. This is described in the relevant chapters.
2. **Sync Timeline group to incoming TC.**
3. **Sync a Timeline to its Timeline group.**

## Receive external timecode

Refer to [**Audio Input**](/integrations/audio.md), [**MIDI Receiver**](/osc-and-midi/midi.md) or [**Receiving DMX** ](/dmx/dmx-in.md)user docs to learn how to do that.

## Sync Timeline group to incoming timecode

<div align="left"><figure><img src="/files/eXY3IfW5k4aJwAhhU9B4" alt=""><figcaption></figcaption></figure></div>

Once you are receiving your MTC, LTC or Art-Net timecode, the next step is to select the **Timeline group** you'd like to sync to it.

<div align="left"><figure><img src="/files/r0gy3E6TxfVmwNVwMCv7" alt=""><figcaption></figcaption></figure></div>

In the **Source** dropdown select the TC Source you'd like to sync to.

<figure><img src="/files/VaXmdk3mRcNUaYHKeH26" alt=""><figcaption></figcaption></figure>

In the Timelines window, you'll be able to see the incoming TC + *Timecode offset*.

### Engaged/Disengaged mode and sync status

<div align="left"><figure><img src="/files/kN0E0P0MQGmY6kqDapNz" alt=""><figcaption></figcaption></figure></div>

If a Timeline group is **Engaged**, it means it will be locked to the incoming TC if a valid one is arriving. In this case, to the right of the Engaged/Disengaged button, you'll be able to see 3 statuses:

1. **No TC source**: this means you haven't selected a Sync source in the Properties of the Timeline group.
2. **No TC**: this means you have selected a TC source, but that TC source is not receiving and TC
3. **Chasing TC**: this means the selected TC source is receiving a valid TC

### Grace period

<div align="left"><figure><img src="/files/6hegz41I88MTkqyeFjXG" alt=""><figcaption></figcaption></figure></div>

If TC stops and you enable **Grace period** in the Properties of Timeline group, LightAct will for the set duration of time assume that TC will resume.

{% hint style="info" %}
**Good to know**: A grace period could be useful to cover intermittent, unintentional breaks in incoming TC.
{% endhint %}

{% hint style="info" %}
**Good to know**: if your TC source is LTC, LightAct includes a bit-flip prevention feature. This means that if, due to audio noise, the incoming LTC suddenly jumps, LightAct will ignore it unless subsequent LTC frames confirm that the jump is intentional.
{% endhint %}

## Sync Timeline to its Timeline group

The steps you will want to follow is to:

1. Determine in which **Sections** you want the Timeline to be synced to incoming TC.
2. Determine their **Start TC** marks
3. Enable **Engaged** status

### Sync sections

<div align="left"><figure><img src="/files/vp34D0Lw0sqIl0Yyi7WN" alt=""><figcaption></figcaption></figure></div>

In the Sync sections part of the Properties of a Timeline, you determine in which Sections you'd like this Timeline to be synced to the incoming TC. You can choose:

1. **Sync in all sections**: all sections will be chasing TC if it falls within them
2. **Sync in selected sections**: only the selected sections will be chasing TC if it falls within them.
3. **Sync in unselected sections**: only the unselected sections will be chasing TC if it falls within them.

#### Section TC marks

Every synced section has a property called **Start TC**. This property determines at what TC will this section start chasing TC.

{% hint style="info" %}
**Good to know**: enable **Show start TC labels** checkbox to see how Start TC times are set up.
{% endhint %}

There are 2 types of determining the **Start TC** of every section:

1. **Automatic**: Start TC is the same as that section's position in the timeline. For example, if section starts at 00:01:50:23 of the timeline, its Start TC is also going to be 00:01:50:23
2. **Custom**: if you choose this type, then you can set up a custom Start TC time.

{% hint style="info" %}
**Good to know**: if a section with an Automatic type is positioned AFTER a section with Custom type, its Start TC time will be calculated based on the time difference between the start of the section with the Custom type and its own.
{% endhint %}

{% hint style="info" %}
**Good to know**: if a section has a Custom **Start TC** time and it's selected you can nudge the Start TC time by one frame with Ctrl & + and Ctrl & - shortcuts.
{% endhint %}

### Engaged/Disengaged mode and sync status

<div align="left"><figure><img src="/files/VvFaTl6JDqpHlJ5BIzcM" alt=""><figcaption></figcaption></figure></div>

To sync a Timeline to its Timeline group, simply switch its sync mode to Engaged. In this case, there are several different statuses that a Timeline can be in:

1. **Group not chasing TC**: this status means that the parent Timeline group is not chasing any TC, so the Timeline also isn't.
2. **Chasing TC**: this means that the Timeline is chasing incoming TC.
3. **Outside synced sections**: this means that the incoming TC does not fall within any synced section.
4. **Ignoring TC**: this means that the incoming TC falls within a synced section, but there was a manual trigger that caused the timeline to temporarily ignore the TC. Manual trigger means manual pressing of one of the play state buttons (play, pause etc.) a cue trigger or something else. If the incoming TC jumps and is still within a synced section the Timeline will start chasing the TC again.