Configure timecode (LTC)

Linear Timecode (LTC) is a clock stream that can be supplied in a number of ways. It is typically used for synchronization in video production, filmmaking, and live events.

We can use it to facilitate automated execution of Cue Actions, through the Pixotope Event System. If we feed multiple engines the same Timecode signal, they will all trigger at the same time - imperative when frame-perfect accuracy is required, for instance for hitting lip sync or matching audio cues!

LTC can also be used to synchronise video and tracking together, or when recording incoming tracking data.

We receive an LTC signal through the video card, either:

• via an LTC port (as analog audio on a breakout cable) OR

• via an SDI input (embedded into the video signal)

In a production environment, this signal would usually come from audio, especially if events had to be triggered on audio playback cues. However, we can easily set up a test environment where we generate and handle our own timecode.

Setup for AJA video cards

Analog audio timecode

AJA Kona 4 and 5

For the Kona 4 and Kona 5 cards, analog audio timecode can be received on the “LTC In” cable on the multifunction breakout cable. 

The state of the Timecode can be seen on the AJA ControlPanel, by viewing the Timecode tab and selecting the source as “LTC Port”. if timecode is received, it is displayed in the control panel.*

*Note the timecode display does not update in real-time, but refreshes every second.

AJA CORVID

For the CORVID video cards there is a joint Genlock/LTC In analog connector. 

Pixotope does not genlock to Timecode and always requires a genlock reference as analog black/burst or tri-level, or to genlock from an SDI input reference signal. 

We suggest for the Corvid cards it is easier to genlock to an SDI input and to reserve the “genlock/LTC In” input for LTC.

N.B. It is possible to construct an auxiliary LTC input cable that connects to header pins on the Corvid series of cards if you need to use both analog genlock and analog LTC concurrently.

Testing LTC Input

It is very simple to set up an LTC source. You need:

• Windows computer with a headphone audio output

• Source audio file 

• Program to playback the file 

• An audio cable from a 3.5mm plug to a BNC connector

We suggest you plug in your headphones to the audio output to verify the signal. Test first that you can hear Windows alert sounds. You may need to adjust the Windows audio mixer controls.

1. Create or download an audio LTC file

   • This should be in .wav format and at 44.1kHz. For ease of testing, we have supplied some working test files here: https://drive.google.com/file/d/1JqEY30n9tOAOMLDz6dN7Exp7XGByLIdr/view?usp=sharing

   • Alternatively, you can create your own file at this site: http://elteesee.pehrhovey.net/ltc/create

   • An LTC file has to be created in the same time base that your video is using - so for 25 or 50Hz video rates, choose a timecode base of 25; for 29.97 or 59.94Hz video rates, choose a timecode base of 29.97

2. Select a program to playback the file

   • Windows Media Player is sufficient. You could also use Audacity: https://www.audacityteam.org/download/

   • Play one of these LTC files back through the headphones - the sound should “warble” quite loudly - timecode has a very distinctive sound

3. Connect the audio cable

   • Connect the audio cable from the headphone output jack to the “LTC In” connector of your AJA card

4. Open the AJA ControlPanel

   • Select the Timecode tab and set the source to “LTC Port”

     • Ensure that the Capture block is showing the correct timebase, and change it if necessary

5. Play the file

   • Play the LTC file again and check that the timecode display is showing the correct value in the AJA ControlPanel

If the correct timecode can be shown in the AJA ControlPanel, Pixotope will be able to access the LTC values.

Windows Media Player can run the LTC .wav file by just right-clicking on the .wav file. If you want more control or to adjust or trim the signal, then we suggest using Audacity.

Troubleshooting LTC Audio

Run the LTC input:

• If the timecode isn’t shown in Pixotope, check that the timecode is shown in the AJA ControlPanel

• If it is not shown in the AJA ControlPanel, check that “LTC Port” is selected and that the sync rate of the Capture block matches the LTC file rate

• If it still doesn’t work, check the audio output of the source computer on headphones. Is it warbling like timecode? Is it loud?

• If it sounds incorrect, or you have no sound, check the Windows Audio Mixer options or try a different LTC file

• If it doesn’t appear to playback in Audacity, check with Windows Media Player

Connecting Audio LTC to Multiple Pixotope Engines

The AJA Kona 4 and Kona 5 cards have an “LTC In” and an “LTC Out” cable, so that Audio LTC could be looped through one machine to the next in a “daisy-chained” configuration.

This is not the best way, however, because any break in that chain could stop the downstream machines from receiving the LTC signal.

A better approach is to distribute the LTC signal through an audio distribution amplifier (d/a), and provide a separate cable from the d/a to each of the “LTC In” ports of the AJA cards.

Setup for Blackmagic Design DeckLink video cards

Blackmagic Design DeckLink cards are supported in Pixotope. At present, DeckLink cards only support timecode embedded in the SDI input.

Using timecode in Pixotope

Setup in Director

1. Choose your primary timecode source in SETUP > Calibrate > Syncing > Timecode sources

   • If needed add a secondary source

Only one embedded source is possible at any time.

For AJA, you can verify that timecode is received, by viewing the Timecode tab of the AJA ControlPanel

• Embedded LTC: set source to “RP188 LTC” or “RP188 VITC”

• LTC Port: set source to “LTC Port”

Setup in Editor

1. Access the timecode using the "Get Video IO Timecode" blueprint node

   • the index refers to primary or secondary within Director