Lining up pictures with the sound | Docs

Every camera reaches InterDirector a little late, and each by a different amount: a USB camera, an NDI camera, a phone over the internet. The sound from the stage microphone usually arrives sooner still. Sync Cameras and Audio measures how far each camera’s picture is from the sound, and works out the sync delay each source needs so that lips and voices match on Program. It takes two people: one on stage with a phone, one at InterDirector.

Get ready

Choose Tools ▸ Sync Cameras and Audio….
On stage, open interdirector.com/sync on a phone. Go through its short checklist: brightness all the way up, volume up on the phone’s own speaker rather than Bluetooth, silent mode off on an iPhone, and the screen facing the cameras. Test beep plays the beeps once, without flashing.
In the window, choose the Sound everything is timed against, usually the stage microphone or the desk, and tick the Cameras to line up: all of them to begin with.
On the phone, press Start. It flashes white and beeps in an uneven rhythm, shows how long it has been running, and stops when you double-tap it. Hold it where the cameras can see it, close to the microphone.

The window watches before you measure. The sound row says whether it hears the beep, with a meter of how loud it is, or what to do: turn the phone up, bring it nearer the microphone. Each camera has its own small picture, with a box where it sees the phone, and says whether it sees it, sees something flashing but not the phone’s rhythm, or does not see it at all, and what to try. Wait until the rows you want to measure are green.

Measure

Press Measure. It takes ten seconds.

Each camera then says how far its picture is from the sound: “Picture 120 ms behind the sound”, or ahead of it, or “In step with the sound” when it is within a frame. When the cameras cannot all see the phone at once, keep them all ticked, turn the phone to each in turn and press Measure again: a camera keeps its last reading in which it saw the phone, and the readings are kept together in one list.

Other sounds

Under the cameras, Other sounds lists every other source with sound, such as a second microphone or a feed from the desk. Tick the ones to line up and they are measured at the same time, by the same beep: “Sound 40 ms behind the reference”. A camera’s own sound always stays with its picture.

Set the delays

Beside the sound, each camera and each other sound is its delay now and the delay that lines it up, such as 0 → 140 ms. Nothing can arrive before it does, so a source is lined up by holding the others back: when the pictures are behind the sound, the sound waits for the latest of them, and each faster source waits the difference. The suggestions are worked out from the whole list, so a camera measured later, and further behind, raises the others’ too.

Press Apply beside one source, or Apply All. A delay can be at most 4 seconds; one beyond that is shown in orange and not set. After Apply, the window measures again by itself, so each source says whether it is now in step. A reading taken before a delay changed says it is out of date.

Reset forgets the results, to start again. Reset and Clear Delays does that and also sets the delay of every ticked camera and sound back to 0, after asking. The reference audio delay stays as you set it, and other sources keep theirs.

You can also type a delay yourself, in a source’s Input Settings.

Reference audio delay

At the top of the results is the Reference audio delay: the delay of the sound everything is timed against. If you know what it needs in this venue, say 63 ms, type it and press Return or Apply, and click the lock beside it.

Locked, measuring never changes it: every camera and sound is fitted around it. A camera so far behind that it would need less than no delay is said, with the least the reference delay must be, and Raise to sets it.
Unlocked, measuring may suggest a delay for the reference too, the smallest delay of all at 0.

Changing the reference audio delay later, say from 63 to 200 ms, moves every ticked camera and sound by as much, so they stay in step with it and with each other; their readings stay true. If lowering it would need a source to go below 0, InterDirector says which and by how much before you go ahead: that source stays at 0 and is out of step until the reference delay is raised again. On air, a change makes each picture and sound jump once, as any delay change does.

The sound, the ticked sources and the lock are saved with the Show.

Moving everything together

Once everything is lined up, Move all by moves it all together, once: type an amount in milliseconds, negative for earlier, and press Apply. With a sound, the reference and every ticked camera and sound move by it; with cameras only, every ticked camera. They stay in step. One that would need less than 0 is said first, and stays at 0 if you go ahead; one that would go past 4 seconds is refused.

Cameras only

To line up the cameras without a sound, choose None — cameras only as the Sound. The cameras are then timed against each other, from the phone’s flashes alone: the latest camera keeps its delay, and every other is given what holds it back to meet it. No sound’s delay is changed, and the phone’s volume does not matter. If the cameras cannot all see the phone at once, turn it to each and measure again, as before, but keep the phone’s page running until the last one is measured: starting it again moves the flashes, and the cameras measured before it no longer compare.

How close it gets

To about one frame of the camera: 17 ms at 60 frames a second, 33 at 30, and a few milliseconds between two sounds. Sound travels about 3 ms a metre, so keep the phone near the microphone. The page corrects for the phone’s own sound delay as far as its browser reports it; a Bluetooth speaker adds more than it reports.