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 Genlock VS Framesync 
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Post Genlock VS Framesync
There is a critical difference between Genlock and Frame Sync; Genlock ensures the frames are delivered at the same time while Frame Sync is that the correct frame is delivered. In Hippotizer Frame Sync is achieved with the Sync Component. For a projector blend Frame Sync is needed, but not Genlock, while hard-edges on an LED wall or 4K display require both Frame Sync and Genlock.

Genlock is a commonly used system in broadcast applications, and is an option on Hippotizer V4. Here we will discuss what it means in the context of Hippotizer and when it should be used.

Genlock (or generator locking) is a technique to synchronise the video frame creation of a video system such as a camera or media server. As a video stream is nothing more than a series of still images transmitted many times per second, the timing between these images becomes very important. A standard video stream for Europe for example, is 50 frames per second (50Hz) which means there is a frame every 20 thousandths of a second (milliseconds or ms). When a Hippotizer creates a 50Hz video signal, an on-board clock counts 20 milliseconds between each frame. Every device creating video has such a clock, and indeed nearly every other device in the signal chain will have a clock as well: such as distribution amplifiers (DAs), cameras and displays. In this way, every device creates the correct frame rate, but it presents the video frames at different times to other devices.

In a normal projection application this ‘freewheel’ works system works very well: the 50Hz signal from the Hippo travels down a cable to the projector which then displays the video on screen. That the same frame arrives at the other projector one or two milliseconds earlier doesn’t matter.Two or more projectors blended to one image doesn’t need genlock, as any difference between the signals is less than one frame which gets lost in the overlap and blending. All that is required is that the content is played back in frame sync, which is to say all the outputs are showing the same video frame at the same time. (This is accomplished in Hippotizer with the Sync Component).

Genlock becomes critical however in applications where two or more video streams must be delivered so that the frames arrive at exactly the same time. A single LED video wall driven by two different processors is a common case. Here a small difference in frame alignment can be seen on fast moving content as ‘tearing’. Another common use for Genlock is with multi-input devices such as a 4K display that uses four HD feeds to make the full 4K image. In these cases it is critical to Genlock the Hippotizer.

With Genlock, there are two options: an internal or external source (house sync). Internal Genlock simply ensures that all the outputs of a system are generated at the same time. It does this by using one of the outputs as a sync source. External Genlock uses a sync signal sent to the Hippotizer by a Sync Generator which can be either a black burst or tri-level sync. External sync is commonly used in television studios where every device from the cameras to the displays will be locked together.

Genlock is configured from the AMD Catalyst control centre. In order to work correctly, all displays should have Identical EDID; which can either be set with the Green Hippo Mimic EDID managers or with AMD’s EDID Emulation.

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Peppe Tannemyr
SSR Beacon DigiGobos®
Sweden retailer of Hippo systems


Wed May 06, 2015 6:14 pm
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