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2 videos timing shifts a bit. How to fix?
http://forums.luma-touch.com/viewtopic.php?f=25&t=7267
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Author:  artemaminov [ Sun Nov 11, 2018 9:00 pm ]
Post subject:  2 videos timing shifts a bit. How to fix?

Hi. I have 2 video tracks. They are captured with different devices. When I match frames to be in sync, after about a minute they becomes unsync again. Tried to use speed change and cheked that clips are same frame rates.
Any suggestions?

Author:  artemaminov [ Sun Nov 11, 2018 9:02 pm ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

1 clip is 30 fps, 2nd is 29.92 fps
So I created new project, import 2nd clip and export with 30 fps.
Nothing changed

Author:  mramosch [ Sun Nov 11, 2018 10:30 pm ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

Could you just for the sake of completeness reboot your iPad and create a new 30 fps project in LumaFusion, drop in the two files (with their full length) one above the other on video track 1 and 2, both starting at 0:00 and then check for a correct sync again - without changing anything else? If you are still experiencing the same problems report back the following settings:


1. What are the base settings of the project? 30/60 fps, aspect ratio?

2. What are the native settings of both files? fps, aspect ratio, file length ?

3. Do both clips have audio and video?

4. Which version of LumaFusion are you on - see LumaFusion/Help and Settings (1.7.834 e.g.) - which version of iOS - see iOS/preferences/info?

5. Do both clips involve the whole file or are they trimmed at the start or ending?

6. Assuming that you always start playback at 0:00 - how much is the drift approximately after one minute and which of the two files is ahead in respect to the other file?

7. Is it constantly the same amount of drift or does it vary, assuming that you always start playback at 0:00?

8. When you stop and resume at ~50 seconds, are they in sync again or still out-of-sync?


And just in case your two files do have different base fps, could you exchange the two clips with each other? Like having clip 2 on the 1st video track and clip 1 on the 2nd video track. Then check again point 6 to 8 of the list above...

Author:  mramosch [ Mon Nov 19, 2018 3:49 am ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

Have you found a solution or was it eventually just a user error on your part?

Please drop a short comment and let us know just to restore our 100% confidence in LF’s engine being solid as a rock.

Or even if you just needed some further assistance...

Author:  Dave Barton [ Mon Nov 19, 2018 4:50 am ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

My guess is post #2 answers the question

Shoot both at 30fps or 29.92fps if you don’t, after time, something is going to have to add or drop a frame hence it will go out of sync?!?

Can you shoot one at an exact multiple eg 30 and 15 or 60 and see if it goes out of sync then?

(Pretty much the same as mramosch was saying actually ;) )

Author:  mramosch [ Mon Nov 19, 2018 6:01 am ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

Actually I am expecting LF to stay in sync regardless of which combination of different fps files I throw on whatever timeline.

1 second is 1 second no matter into how many sub parts it is divided, this being frames. So even a 29.92 fps file has to throw in a frame every now and then in order to compensate for the missing 0.08 frames.

My guess is that the last (partial) frame (0.92) of a 29.92 fps clip in a 30fps project is just displayed for the whole frame. This way there is no drifting over time, no frame drop respectively frame insert necessary.

LF does not do any interpolation for half-frames or sub-frame values, just adding or dropping frames - no matter what ratio.

So I am pretty curious what the problem in the OP is...

Author:  artemaminov [ Sun Nov 25, 2018 7:11 am ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

Find out that it is a dvr issue. It’s dropping frames when rx signal is low.

Author:  artemaminov [ Sun Nov 25, 2018 7:13 am ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

Recording at Fatshark HDO FPV goggles

Author:  sfdex [ Sun Nov 25, 2018 12:27 pm ]
Post subject:  Re: 2 videos timing shifts a bit. How to fix?

I’ve found over the years that differing frame rates of source material is almost always going to cause headaches. I’ve used Premiere Pro since long before it became Premiere Pro, used Media 100 back in the day, occasionally use FCPX and Avid, and all of them have difficulty with differing frame rates on the timeline. Just expecting an application to handle different frame rates as if they’re all the same (one second is one second, no matter how it’s split up) isn’t realistic. Progressive-frame video on computers (and iPads/iPhones) isn’t handled in seconds, it’s handled in frames.

Smart phones aren’t always exactly consistent in the frame-rate at which they capture video, and other devices vary, as well. There’s also something called drop-frame and non-drop-frame, which is why some devices that purport to be shooting at 30 FPS actually record at 29.97 FPS, or rather than 24 FPS actually records the footage at 23.976. For the most part, and particularly on short movies, having slightly different frame rates on a timeline won’t have much impact on your work, but sometimes after a bit, there is a synchronization slip, as the original poster stated.

Premiere Pro and AfterEffects give you the option to “interpret” the footage — that is to impose a specified frame rate on the footage. (Other pro desktop apps offer the same feature, often called by other names.) So, if your device captured at 29.97, but your timeline is 30, you can interpret the footage to be 30. The software speeds the footage up by a little less than 1%, which is imperceptible to just about every human on the planet, and it allows 29.97 footage to stay locked in sync with 30. iOS handles video a little differently than MacOS or Windows, so “interpreting footage” may not be possible.

The best solution is to ensure that you’re capturing all your source material at the same frame rate. Obviously, sometimes you can’t control the exact frame rate, and when that happens, you just have to jump through a few hoops to make things line up, whether your using LumaFusion or Premiere Pro or FCPX; it’s just a property of how media files work.

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