Synchronized from the Start: Genlock in Broadcast
Timing is everything for live video broadcasts. Your viewers want to be close to the action, by watching it as close to real-time as possible, in the best quality possible. And to minimize delay while maximizing quality, synchronization is important – especially for remote production where multiple cameras are used. Genlock is one of the critical tools to help ensure synchronicity, right from the beginning.
In this blog post, we are going to explain what genlock is, how it works, and why it is so important for your broadcast workflows that rely on multiple cameras, including remote production.
A portmanteau of “Generator Locking,” genlock ensures that all of your audio and video capture devices are synchronized. Genlock is typically used to synchronize cameras, to ensure that they are all perfectly synchronized to a single clock.
With genlock, you have something called a “master” device – this can be either an external timing device used exclusively for genlock, or one of your cameras. The rest of your devices are connected to this master device. Through this connection, (most broadcast cameras have an SDI input specifically for this,) the master device puts out a signal to keep every other device synchronized to the master clock.
Using a genlock device will also give you the ability to keep your audio feed synchronized to the same master device, ensuring that your audio and visual information is precisely synchronized with each of your video feeds.
Keeping it Together – Why Synchronization Matters
There are many elements that make synchronization an important element of the broadcast viewing experience, and genlock addresses many of them at the source. As a broadcaster, you want to ensure that your audio and visual aspects are not only synchronized in timing, but in quality, to give your in-studio production team the ability to switch between camera feeds seamlessly.
One of my pet peeves, as a broadcast viewer, is when the audio isn’t synchronized with the visual. It doesn’t take very much for there to be a noticeable loss of sync between your audio and visual feeds – many viewers will notice if the offset is as little as one or two frames. And once they notice, they will continue to notice for the rest of the broadcast. It’s even more of a challenge for producers and engineers, who need to spend extra time on re-synchronizing sources, instead of focusing on the other elements that make an excellent broadcast.
The human eye perceives information incredibly quickly. Up until recently, it was presumed that people could process information in as little as 100ms, but a new study from MIT has suggested that it is much quicker – as little as 13ms, which is shorter than the 16.67ms duration of a 60fps frame. Unless your feeds are well synchronized, changing between camera angles could result in what is known as a “jump,” when the display re-adjusts the horizontal and/or vertical scan to reframe the image. In the best-case scenario, it might be a small “blip” that is barely noticeable, to viewers, but in the worst case, it could be a critical moment that your viewers miss.
Out-of-sync frames aren’t the only concern for broadcasters in synchronization. An important role of a genlock device is to keep the cameras synchronized. Different makes and models of cameras will have hardware designs, performance capabilities, and also clocks, and unless you can ensure that they are all synchronized, your cameras will become increasingly out of sync over time – also known as drift. Not only will this look odd when switching between camera angles, it will create a host of problems, especially if you’re using interlaced video.
Just the Beginning
In remote production workflows, genlock is just the first step in ensuring that your video feeds are synchronized. Fortunately, the next steps won’t need to be prohibitively expensive, as broadcasters can synchronize their video source over the internet – especially useful for live events. Want to learn about how you can ensure that your video feeds are synchronized in remote production? Download our white paper, Synchronizing Video Sources Over the Internet for Live Event Coverage.