Variable Frame Rate

[Davidk]

Scattered thru the forum pages (this year esp but earlier as well) are various comments about 'variable frame rate' and the impact (bad) on VS. With the way mobile (smart) phones have taken over the low-end of video recording devices, it seem desirable to know a bit more about 'variable frame rate'. I've searched forum using a key of variable+frame+rate (several ways) but the results are neither good or specific. The search engine could probably be improved a lot.

So I have a number of questions on this subject I'd appreciate answered by someone who knows:
1. Why do it? (I've speculated but that's not knowing). Obviously (some) mobile devices are the main culprit now, but are there other participants in that measure?
2. How does one detect a variable frame rate from review of the clip properties?
3. A fixed frame rate has been the empirical basis of display standards since Moses. As those mobile phones play the variable frame rate images back on the device without any apparent (none commented on) impact on the imagery as perceived by a human eye, clearly they incorporate an internal converter as part of that process. For use with VS, software that does a conversion to a fixed frame rate has been the pretty much universal recommendation. So, what software is there available to do that?

Davidk

[asik1]

David, check this tool
https://mediaarea.net/QCTools
might gives you few hints

[Davidk]

Hi asik,

At 1st glance looks like a video equivalent of audacity, better documented. But nowhere in there was any discussion that even remotely looked like a method of converting a video clip with variable frame rate to a fixed frame rate.


Davidk

[MrJohnny]

Hi David

Search the web for "why variable frame rate"

https://stackoverflow.com/questions/120 ... ding-video

https://bronami.video/gopro-low-light-s ... ps-tricks/

https://forums.androidcentral.com/htc-o ... rding.html

Seems there is possible confusion where some authorities believe a camera that can accommodate the photographer changing the frame rate to a non standard (constant) or different frame rate qualifies as variable frame rate. So you have got to be careful.

1 Why use VFR? - Slo Mo, poor lighting conditions, may be other reasons, all to get better quality/reduce artifacts.

2 How do you detect VFR? - MediaInfo or GSpot.

3 What S/W to convert to CFR? - HandBrake, FFMPEG or a myriad of other convertors, take your pick, exercise care!

Some NLEs deal with VFR others not so much. A major side effect can be out of sync problems.

John

[asik1]

Hi asik,

At 1st glance looks like a video equivalent of audacity, better documented. But nowhere in there was any discussion that even remotely looked like a method of converting a video clip with variable frame rate to a fixed frame rate.


Davidk

This is analyzing tool

[aljimenez]

To me the only reason for variable frame rate is file size and/or lower bit-rates. But as you say, this is the future since smartphones are so dominant. VS will have to handle these files hopefully by next version.

[Davidk]

1. My (un-stated) speculation would have been wrong. Like Al, I thought RAM/file size seemed the probable reason. However, all the on-line commentary has been about low light levels and the related fixed focal length of the lens in these phones. No doubt the result is a compromise engendered by the thin frame of the phone that caused the choice of a real small lens: of fixed aperture/focal length around f2.5. That is, optimised for near images, and not really suited to any longer distance pictures. An electronic zoom and software compensation would off-set some of that. And while f2.5 is good (better than f8) in low light, clearly slowing the shutter speed down to get a picture of some sort results in an overall lower frame rate for video.

And since anything lower than about 15fps looks blinky or stuttering (lots of research about 40 years ago on this - around the time when the slow cpu was doing all the work managing data on displays, before video cards or chips came along - slow rates seen by eye esp about 8fps interfere with brain waves and cause serious headaches: health hazard), a lack of any commentary on that means some method of increasing the frame rate when that captured video is played on the phone must exist.

2. File analysis tools are useful but if you don't know what to look for, and its not documented or intuitive, probably a waste. Haven't seen anything yet that would tell that clip was vfr, other then indirectly eg VS crashing.

3. Researching the conversion rate tools so far mentioned . . . .

Davidk

[lata]

Hi David

Variable frame rates, viewing the properties of the video within Video Studio shows the frame rate.
If that rate is different to the standard rate, 25, 29.97, 59.94 etc, maybe 29.85 then it is most likely the video is using a variable rate.
Media Info shows the video frame rate as variable, don’t think I have a sample on my pc to check that.

[TonyP]

I've used Handbrake to convert variable frame rate to constant frame rate, or even problematic video.