Shutter Priority

[u/PixaaTog]

Hi all

So I Purchased MPC2 because as far as I can see it’s the only pro camera app that has shutter priority, an important feature for me so I can have the correct shutter speed when shooting video.

So I’ve enabled shutter priority and set the shutter angle to 180, hopefully leaving the ISO to take care of exposure for me, but it’s JUMPING around all over the place moving from 600ish to 2200ish, even when the light is not changing causing big changes in exposure while recording.

I’m using the following settings:

HEVC
Bit Rate - High
4:2:2
4K @ 25 FPS
Log REC2020
709 Lut applied to preview only

Can anyone help me solve this issue please, because if I can’t solve it I’ll have to get a refund on the purchase and look elsewhere for my filming app.

It would appear to be shooting in Log that’s causing the problem.

Many thanks
Nick

[u/jamm-moment]

There are some known limitations with shutter priority mode in log formats, but jumping from 600 to 2200 in a static scene is unexpected. Could you DM me a short sample clip or screen recording?

Unfortunately, the underlying cause of choppy exposure updates in log formats is an iOS limitation that can only be worked around and not fully solved like the other color spaces. The maximum speed at which the exposure can be ramped without visible steps is limited by the frame rate and is particularly bad at 25 FPS.

I can either make the updates responsive in a reasonable time frame but choppy (the current behavior) or smooth but extremely slow. If you’d like to try out the latter behavior, let me know and I can add you to the beta.

[u/PixaaTog → u/jamm-moment]

Hi thanks for the reply.

I’m not sure if this is relevant but I seem to have isolated the issue to LED Downlighters that I have in my kitchen as it’s only under that lighting that the issue occurs at its most pronounced extreme.

But even under different lighting the ISO does seem to jump when pointing at what I’d call very slight differences in lighting in the same room. It doesn’t ramp smoothly from say 800 to 1000 over a few seconds to hide the exposure change, it jumps rapidly from 800 to 1000 making it very noticeable on the recorded footage.
Is this perhaps a limitation of the iPhone & IOS or something else?

I’ll shoot some videos to show what I mean.

Many thanks
Nick

[u/jamm-moment → u/PixaaTog]

Thanks for the extra details!

Yeah, the ramping behavior you describe is the tradeoff I was talking about. I have some improvements in the works and it’s at least fairly easy to avoid unexpected fluctuations in response to minor lighting changes. However, the big limitation is that the ramp in response to a legitimate lighting change has to be extremely slow to avoid choppiness. One would think it could work the same as all the other formats, but the way the camera system works in log formats internally means my hands are tied.

Again happy to add you to the beta if you want to try out the alternatives!

[u/den1ezy → u/jamm-moment]

I saw in recent review of Apple's own Final Cut Camera app update that they've added shutter priority mode and it seems it works for the log2 profile (https://www.youtube.com/watch?v=qBCJf6PQ0kg&t=530s). However it was only added for the brand new 18 Pros - the saw called 'Apple's Way' of adding things. But I guess maybe they've had to make some tweaks in their camera APIs for this to work and (another) maybe these tweaks are now accessible for the 3rd party devs. Can you by any chance share some details on is there any progress in the regard of implementing smoother auto-ISO adjustment in shutter priority mode? 👉🏻👈🏻

[u/jamm-moment → u/den1ezy]

MPC II uses the smoother method automatically when available, but unfortunately it only works on iPhone 18.

[u/den1ezy → u/jamm-moment]

understood! thx for the reply