Why is there strobing?

[Evgeniy_Kolobov8026]

I slow down the original 50fps video by half and set it to 50% in a 25fps project, and everything slows down smoothly and beautifully.
But when I slow down the original 59.94fps video by half and set it to 50% in a 25fps or 29.97fps project, I see a slight strobing in the video. Optical flow is used in all versions. Why is there strobing?

[Averdahl · Accepted solution]

Because there is a mismatch between the 59.94 fps footage and the frequency in the electical system/electrical outlet.

If you have 240V 50Hz in the electrical outlet and shoot 50 fps video it matches and slow motion will be great. (50/50=1)

If you have 240V 50Hz in the electrical outlet and shoot 59.94 fps video it don´t match and the slow motion can be strobing depending on the lights used. (50/59,94=0,8341675)

The opposite goes for 50 fps footage shot when the lights are fed with 110V 60Hz.

Why is there strobing?

By @Evgeniy_Kolobov8026

[Evgeniy_Kolobov8026]

so in my region, you need to shoot in PAL and only in 50 frames, and then slow motion video will be smooth? Right?

[Averdahl]

In short, yes.

Smooth slow motion should be able with 59.94 in PAL land as well, but there is a high risk for strobing/pulsating lights when shooting indor with electrical lights as the source of light.

So if you get un-smooth slo-mo, iow no strobing, it can also be due to the fact that a sequence with 50 or 25 fps not always play well with source footage with a fps that not divide evenly with 50 or 25.

What issue do you have, un-smooth slo-mo or strobing/pulsating lights, or both?

so in my region, you need to shoot in PAL and only in 50 frames, and then slow motion video will be smooth? Right?

By @Evgeniy_Kolobov8026

[R Neil Haugen]

And if the issue is lights strobing due to varying electrical Herz frequency, the best fix is probably Digital Anarchy's Flicker Free.

[R Neil Haugen]

Is is interlaced?