FPV Camera Latency Testing

I have been testing FPV camera latency independently and I share the results here. Latency has an impact on the pilot’s reaction time and stick feel, and it is one of the most important aspects in selecting FPV cameras.

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FPV Camera Latency Measurement

Other parts of an FPV system can also contribute to the overall latency, for example, video transmitter and receiver, but it seems to be insignificant compared to FPV camera lag. Here is my testing on this to prove it: 5.8Ghz Analog VTX/VRX latency

The latency of an analog FPV camera is constantly changing within a certain range. Manufacturers tend to brag about their cameras’ minimum latency, but the average latency are usually much higher, and that why third party testing like this is extremely useful.

Values in ms – milliseconds.

HD cameras as FPV camera:

*HD Cameras are measured during recording.

My Method of Testing Camera Latency

I see many reviewers use a virtual timer on smartphone to measure the latency of a FPV camera or HD camera video out, which is very unreliable in my opinion.

First of all, the display and camera both have relatively low refresh rates, and they are not in sync either. For example if everything runs on 60fps, the result could have an error of up to 16.7ms. This is a significant error margin because the lowest latency are down to 4 or 5 ms in same FPV cameras.

How it works

My testing setup is simple, the FPV camera is connected directly to a display via AV input.

I put an LED in front of the camera, when is controlled by an Arduino board. The display brightness will change as the LED turns on and off. There is a photo-transistor (aka LDR – light dependant resistor) in front of the monitor to detect the brightness changes.

The time difference between the turning on of the LED and change of screen brightness, would be the latency we measure.

The Arduino runs at 10KHz sampling rate, and I take 500 samples at random intervals in each test.

I love this setup because it’s completely automated using scripts.

Possible Errors

The LED and LDR have delay as well: LED takes time to turn on and the LDR takes time to detect light. From my measurement, the delay of these components is less than 120us in total, compared to the delay of our FPV cameras, this is negligible.

The display’s low refresh rate however, will be a more significant contributor of additional delay to our measurements. But since I am taking a very large number of measurements at random intervals, the averaged result should be unaffected by the phase shift. I can confirm the results are consistent and repeatable in my testing.

This testing is definitely useful for comparing relative measurements since the error will be the same across all data samples.

NTSC and PAL

My assumption was that the video format (NTSC/PAL) has an impact on the latency.

NTSC is 30fps while PAL is 25fps, but because they are interlaced (in every frame, odd lines are drawn before even lines), which gives them a real fresh rate of 60fps (16.7ms) and 50fps (20ms) respectively. So in theory NTSC should be 3.3ms faster than PAL.

I want to verify if NTSC is really faster than PAL, and the Eagle is very handy as I can easily change video encoding in the settings. So I tested the Eagle (CMOS) and Eagle 2 (CMOS) under PAL and NTSC.

Here’s what I found:

• With the Eagle, minimum latency decreases significantly with NTSC, while average latency shows moderate reduction, but there is little to no difference in maximum latency
• The above finding didn’t apply to the Eagle 2 though, the latency seems to be the same in both NTSC and PAL

I checked with Runcam, and they suggest the difference in latency could be caused by the camera algorithm, which might perform slightly better with one video encoding format than the other. In this case, the Eagle 1 is faster in NTSC while the Eagle 2 works slightly better in PAL. But video encoding itself doesn’t necessary make a noticeable difference in latency. Therefore to keep things consistent, I will stick to PAL whenever possible in my testing.

Edit History

• 2017 May – article created
• 2021 May – updated article with some more cameras