iOS 17.6.1 BM Camera App 2.0 not recording 25fps video

H.265, HD, rec709, LPCM, 48kHz.
iPhone 15 Pro Max 17.6.1
BMC 2.0.000016

Video shot at 25fps is reported to be at slightly less (ex. 24.98, 24.96) when inspected in VLC or with the MediaInfo tool.
I suspect that very low framerates (24.5, 24.6 fps) also cause audio distortion, which is not audible during recording, but makes the audio (from a Rode AI-Micro) unusable.

24.648448 fps, anyone?

image (2).png (62.47 KiB) Viewed 524 times

Interestingly, shooting off-speed 25/25 gives video running at 25.000 fps (but no audio track..).

No smartphone is recording CFR reliably, even if the iPhone is getting close as long as you avoid its electronic stabilizers.
The audio issue you may experience will come from this fact, not the fps in general. 48 kHz will always be the same number of samples, independent of frame rate.
It may help to conform the footage to 25 fps with ffmpeg oder Shutter Encoder.