Frame rate w/ this Sony speed camera

[heath_hays]

I've got a strobe light I'm trying to figure out what exact frequency it's flashing at, and already being outclassed by my Canon EOS T7, I decided to hop on Amazon and pick up a Sony Cyber-Shot RX10 IV and to see if I could high speed frame rate capture some of these strobe flashes. I know just enough about either of these two cameras to be dangerous, so I had to look up on youtube to see EXACTLY how to set this Sony camera up to do the specific high speed shot I needed. Luckily I ended up figuring it out and now I have about 20 seconds of slowed down footage I need help analyzing.

Since the thing I was filming was a light source itself, and resolution didn't matter I was able to use the highest frame rate setting on the camera, which I believe was 960, even though I thought I had seen the frame rate advertised as 1000 somewhere. This might have something to do with NTSB vs. PAL possibly?

So now that I've got about a second of flash time recorded at that high frame rate (in the form about a 1MB mp4 on the SD card), what free editing program can I download and use to view this video and analyze this light's flash rate?

Thanks.

[Ed_Ingold]

Measure the flash rate using an oscilloscope and a photo diode.

[conrad_hoffman]

Of the various ways to do this, a video is about the last method I'd choose. The problem is you don't know if the sample rate (frame rate) is fast enough to get all the flashes, or some are missed between frames. If the strobe makes a noise when it fires (tube type, not LED) I'd record it at a high sample rate and then analyze the recording using Audacity (free sound editor). If the rate isn't too high and you have a turntable, put a narrow white strip of tape on a record and take a picture of exactly one revolution. Count the number of stripes and calculate the rate, knowing one revolution is 1.8 seconds. Best way is scope and photodiode. If you've got something like an old General Radio strobe, that will be about the only good method, though those have built in calibration compared to line frequency, so little need to measure.

[Ed_Ingold]

Another method would be to make a white mark on a black disk, put it on a record turntable at 33-1/3 rpm, and shoot with a 1 second shutter speed. That would produce an image of multiple lines, which you could then count. If the lines overlap, find something which rotates faster, and use a shorter shutter speed. The results would be as accurate as your shutter, typically +/- 10%.

Edited December 25, 2022 by Ed_Ingold

[rodeo_joe1]

You can turn the mic. or line audio input of a computer/laptop into a simple oscilloscope. Just connect a photodiode to a 3.5mm jack plug and use the free 'Audacity' program to record a trace of the light pulses. They'll sound like a series of clicks or a buzzing noise, which can be seen as a series of spikes or pulses in Audacity. 

Simply zoom in (magnify) on the time axis and you can get a very accurate view of the pulse duration and frequency. 

Edited December 27, 2022 by rodeo_joe1

[heath_hays]

Thanks for the great suggestions guys.  If I had just a little more experience in some of those directions I'd go that route, but a few have suggested analyzing my video with DaVinci Resolve so that's what I'm trying first.  I loaded my ~4sec 1GB .MOV file into Windows Media Player and video looks like it would do well with closer inspection.  The entire video takes 2m 35 sec to play out and there's an 18 sec segment somewhere in the middle that captures 7 flashes.  The light stops flashing after that so 7 will have to do.  But the flash and subsequent dimming of the element look so smooth I'm sure I've got enough for a precise frequency measurement once I'm able to look at this frame by frame.

So I installed DR on a HDD starved computer and tried to load my file up but like a monkey on a piano I never hit the right combination of buttons to get my file up like I wanted.  Could anyone coach me on how to import my .MOV into DaVinci and do this quick analysis?

[heath_hays]

Update is I finally figured out the flash rate.  It wasn't with Resolve though.  I ended up using an online program someone suggested called VSDC.

So now, I need to confirm my video was filed at 960 fps.  To make a long story short, it could be either 960 or 1000 fps.

How can I figure out my video's fps?  Is there any kind of meta file it has associated with it that lists fps, sort of like viewing a file's properties?

Edited January 15, 2023 by heath_hays