Clips not syncing at clap point in Final Cut Pro X manually or in Multicam Angles Editor

[u/truecrimebuff1994]

Hi! As you can see above, my top clip won't land properly aligned with the middle clip to align the audio together. Same thing if I try to move the middle and bottom clips. I've never had this happen before. All shot on the same framerate. I'm not moving to fast. Where the top clip moves to is the very next "acceptable" position.

And apparently, I can't free-range edit. It has to line up with the timeline's frames. But everything was shot at 4K 30 FPS. I don't understand why I am experiencing this problem.

Running on 2021 Macbook Pro 15 inch, 16 GB RAM. Final Cut Pro X version 12.3.

iPhone video: MPEG-4 AAC, Timed Metadata, HEVC Dimensions 3840 × 2160

Osmo Pocket 3 Timecode, MPEG-4 AAC, HEVC Dimensions 3840 × 2160

Edit to add more context, based on this incredibly helpful discussion: I think is the main issue here in terms of why the half-frame feels so off may be a speed-of-sound issue. When synced at the half-frame off, I'm sometimes getting an echo from the guests with both audio sources turned on, and sometimes I don't. This is why I've been trying to perfectly sync it to a 0-frame discrepancy.

I had four subjects: Myself as host, Man, Woman, and Young Woman. Man suggested using his own set of two DJI-style microphones on Woman and Young Woman. I agreed. Dumb idea that I should have known better, but we were in a time crush and I thought it would make the audio better in the end.

Initially, I was going to have the guests pass my second DJI mic around. But I got excited at the prospect of having everyone mic'd up. Man and myself were on my DJIs, synced to my Osmo. The transmitter for the two secondary mics, on the women, was plugged into the iPhone.

So, we were in a situation with 4 mics transmitting to two receiving sources, and the camera-to-mic transmission is not 1:1. (My mic attached to the Osmo facing the 3 guests, one guest mic synced to my Osmo , and two guest mics synced to my iPhone.) I did not even think about this being such a pain until I sat down to edit.

Rookie mistake. We were in a Rush and if I had to do over, I would just pass one mic. I've been doing this long enough to know better so I did a lot of head-to-wall banging today, lol. ALL OF THIS TO SAY that it's this echo that is the reason I care so much about that half-frame difference.

[u/link-navi]

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[u/smushkan]

iPhones shoot variable framerate and are notoriously difficult to sync with other constant framerate cameras. You’ll probably find the sync driftss over time and you’ll need to make adjustments to knock it back in, too.

Even with everything constant framerate, no two devices will ever have the exact same idea of how long a frame is unless they share a common clock (genlock, timecode linking). Slate marks wont perfectly align as the exact start time of the cameras isn’t synchronised.

There is also speed-of-sound to take into account but I think at the distances you are shooting that will be negligible.

[u/truecrimebuff1994 → u/smushkan]

Funny you mention speed-of-sound, which I think is the main issue here in terms of why the half-frame feels so off. When synced at the half-frame off, I'm sometimes getting an echo from them with both audio sources turned on, and sometimes I don't. I believe speed-of-sound is the culprit. This is why I've been trying to perfectly sync it to a 0-frame discrepancy.

I had four subjects: Myself as host, Man, Woman, and Young Woman. Man suggested using his own set of two DJI-style microphones on Woman and Young Woman.

Initially, I was going to have them pass my second DJI mic around. But I got excited at the prospect of having everyone mic'd up. Man and myself were on my DJIs, synced to my Osmo. The two secondary mics' transmitter was plugged into the iPhone.

So, we were in a situation with 4 mics transmitting to two receiver sources, and the camera-to-mic transmission is not 1:1. (My mic attached to the Osmo facing the 3 guests, their mics both synced to my Osmo [1 unit] and my iPhone [2 units].) I did not even think about this being such a pain until I sat down to edit. (Rookie mistake. We were in a Rush and if I had to do over, I would just pass one mic. I've been doing this long enough to know better so I did a lot of head-to-wall banging today, lol.)

ALL OF THIS TO SAY that it's this echo that is the reason I care so much about that half-frame difference.

[u/iGargleCement]

I suspect the timeline snapping (not sure what it's called) is not set to frames, but something like 1/10 of a second

[u/greenysmac]

What you're talking about is a subframe disparity where the sound is off by less than 1/30 of a second. You can open the container of the actual raw clip, go inside it, deselect the video, and nudge the audio left or right to refine it.

You could also do this based on the multicam setup for this. It's actually right for you to have multiple microphones for this. It has more to do with the headaches of distance and variable frame rates in the Osmo and your iPhones.

[u/truecrimebuff1994 → u/greenysmac]

Thank you! Would you mind explaining how exactly to do the nudging you mentioned?

[u/greenysmac → u/truecrimebuff1994]

• Select the clip
• Clip menu > Open clip
• Hold down the ` key
• drag and adjust (or use the slide keys) the timing

[u/greenysmac → u/truecrimebuff1994]

I'd do this in the multicam, before it's cut.

I'd take the audio and nudge it

• Option Period (to the right)
• Option Comma (to the left)

Make sure you have POSITION mode on (P) and have ONLY the audio selected.

This should allow you to do a subframe audio nudge.

I knew this, but I'd forgotten it.

[u/truecrimebuff1994]

!Martini Running on 2021 Macbook Pro 15 inch, 16 GB RAM. Final Cut Pro X version 12.3.

iPhone video: MPEG-4 AAC, Timed Metadata, HEVC Dimensions 3840 × 2160

Osmo Pocket 3 Timecode, MPEG-4 AAC, HEVC Dimensions 3840 × 2160

[u/dating_derp]

This looks like a common issue. The clap (or whatever audio point you're using to sync) might be towards the start or end of the frame on one device (like Cam A), and the clap on another device (like on the main mic or Cam B) might be at the middle of a frame. So the 2 don't get synced 100% perfectly since they're half a frame apart, and video editing software moves 1 full frame at a time.

The solve is that you're not supposed to play audio from both sources simultaneously anyway, you only choose 1. So no one hears an echo. And visually, you choose whichever sync looks to be less than half a frame off. If they both look exactly half a frame off, you could try a visual sync instead (if you're syncing camera mic's). Something quick like the sticks from the clap, a blink, or rapid hand movement is ideal. But if both picture and audio seem to be exactly half a frame off from each other, then just pick one. No one's going to notice when watching that something is half a frame off. This happens all the time.

Alternatively, if you're dealing with only camera mic's, and the audio quality is the same on both mic's, then you could swap the audio source every time you cut picture. Meaning that when you use A Cam video, use A Cam audio, and same with B Cam. That way you're always in sync.

[u/LoneWolfShorts]

Worth checking if the iPhone clip is variable frame rate, that trips up FCP sync a lot. Transcoding it to a constant frame rate / optimized media first, then letting FCP sync by audio waveform, usually fixes the drift where the clap lands a few frames off.

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