How much video latency does your OpenROV system get?


Now that a bunch of people are starting to complete their OpenROV builds, we can start comparing notes on how well they perform!

To start out, here's a simple way to test system lag with you're ROV (thanks to Bran Sorem who originally demonstrated a method similar to this) :

1. Boot up your ROV and open OpenROV Cockpit

2. Open a webpage or program that displays time with millisecond accuracy (I used estopwatch), and size the window down so that can be seen at the same time as the Cockpit display

3. Use the ROV's camera to look at the timer

4. Take a screen shot (print screen) of the display so that both the timer and the display in Cockpit are captured

5. Paste the screenshot into an image editing program and move a cut-out of what the timer is showing to be right next to what OpenROV Cockpit is showing

6. Do this several times and continue to paste the screenshots next to eachother

7. Calculate the difference between the time shown through OpenROV Cockpit (looking at the timer) and the timer itself.

8. Post your findings, along with what hardware you're using here on OpenROV!

Here's the data from my test:


Computer: Lenovo Thinkpad W530 running Windows 7 with a 2.7GHz Core i7 processor and 8MB of ram

GPU: NVIDIA Quadro K2000M 2GB

Browser: Google Chrome Version 31.0.1650.57 m


Latency average (6 samples): 0.245 seconds

Standard Deviation: .0491 seconds


I will have to do this when I finish building the ROV.


Good job Eric - I wonder how video latency is related to control latency? But then not all of us have quarter-of-a-second reaction times any more!


What an ingenious method to measure system latency - I'll definitely use it myself in future. It reminds me of the method John Carmack of id software used to measure latency of a head-mounted display (on SuperUser). However, he was using a 240fps camera and counting the frames between a button being pressed and the screen updating.


Laptop Compaq 8510P
Windows 7
Intel Core Duo CPU T9300 @ 2.50GHz

Cockpit Timer Latency
Latency test 1 with tether 4.077 4.366 .289
Latency test 2 with tether 4.977 5.325 .348
Latency test 3 with tether 4.455 4.804 .349
Latency test 4 with tether 1.969 3.936 1.967
Latency test 5 no tether 2.604 2.951 .347
Latency test 6 no tether 0.393 2.718 2.325
Latency test 7 no tether 3.009 3.357 .348
Latency test 8 no tether 3.072 3.303 .231