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audio sync drifting

I am still editing in FCP 7 (on a power mac, OS 10.6.8). I transcoded interview footage from my iphone to Apple PR 422. Both the original and the transcoded 422 footage plays in sync with the Quick Time player, but when I bring the 422 into FCP 7 it drifts out of sync. (The rate of the original and the 422 is 29.97)


I first transcoded using my MacBook's own encoder. When I found the sync problem, I then transcoded using MPEG StreamClip which I've used MANY times to transcode to Apple Pro Rez 422 with no sync drift problems. But no. Ugh. Any help with be much appreciated!!

MacBook Pro 15″, macOS 11.6

Posted on Nov 11, 2023 2:21 PM

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Posted on Nov 12, 2023 11:29 AM

The conversion frame rate is on automatic, basically passing it through, though it can't do it exactly like the original. I can't remember if you can control this in Streamclip, but in Compressor you can specify an exact frame rate, like 29.97 or 30 (fractional frame rates are ridiculous). The output file will be a constant frame rate and more likely, though not certainly, able to maintain sync, because the sample rate is constant.

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Nov 12, 2023 11:29 AM in response to Eve Goldberg

The conversion frame rate is on automatic, basically passing it through, though it can't do it exactly like the original. I can't remember if you can control this in Streamclip, but in Compressor you can specify an exact frame rate, like 29.97 or 30 (fractional frame rates are ridiculous). The output file will be a constant frame rate and more likely, though not certainly, able to maintain sync, because the sample rate is constant.

Nov 11, 2023 4:55 PM in response to Eve Goldberg

Hi Eve. I don't know if converting from 44.1 kHz to 48 kHz will fix the audio sync. It's been so long since I've used FCP7, are you sure the project/timeline settings match the properties of your transcoded file? Compressor, if you have it, can transcode and sample rate convert. Maybe someone else will chime in with a method that doesn't require Compressor. ffmpeg also works but it's more complicated to set up.

Nov 11, 2023 6:45 PM in response to terryb

Used the encoder built into my MacBook. (you just right click on the clip, and one of the options is to encode to Apple ProRes 422.) i’ve done this before and there’s been no problem. But when there was the problem this time I then transcoded it again using MPEG stream clip. Same result. I’ve used MPEG stream clip many many times to do the same transcoding process and never have had sync problems before. And I’ve used the MacBook encoder before with no sync problem.

Nov 12, 2023 7:33 AM in response to terryb

I"m not sure what those things are you mention at the top, but I can research and find out. In the meantime, here is info about the clips:


The 422 clips are: Linear PMC, mebx, Apple Pro rez

The exact same type of clips, created and transcoded on the exact same hardware and software has worked for me perfectly before - many times. Again - both the originals and Pro Rez play perfectly in Quick Time movie, but not in FCP7.


The only change I can think of since I made my last video was updated software on my iphone. When I checked my iphone camera settings, the video is set to 30 fps - no other options. But it shows up (in both the raw and transcoded footage) as 29.97 once it's on my computer.

Nov 12, 2023 7:48 AM in response to Eve Goldberg

Do you have Compressor? You might try that to convert the clips to 29.97 and re-sample to 48K.


i don’t know if Invisor or MediaInfo work in your OS, but try one to check the specs and frame rate of the original iPhone media and the converted file. Which iPhone and format did you use? There are often variable frame rates in iPhone recordings which may make it difficult for the application. especially if the audio is just passed through when converted.

Nov 12, 2023 8:50 AM in response to Tom Wolsky

Thanks. I do have Compressor, but when I've tried to use it in the past I realized that I don't know what I'm doing and don't find it intuitive, so I quit long ago and have used MPEG Streamclip or my MacBook built-in transcoder successfully ever since. I just opened Compressor yesterday again and gave up.


Regarding the iphone footage: I used Image Capture to bring the iphone footage into my MacBook, and when I saw that it was all good (on Quick Time player) I long ago erased all the footage off my phone, so I don't have that. I do know that while the iphone says it shoots at 30fps (no option for 29,97), the raw, un-transcoded footage reads at 29.97 in FC7 and drifts just like the transcoded stuff. For the fun of it, I brought in a few clips from a project I did a couple of years ago (shot and transcoded the same method, on the same equipment) and that footage plays perfectly, no drift, just as it did when I edited it back then.


Ugh! I don't want to just give up and eye-sync each clip once I have a rough cut, but if I have to, I will.


And then, if I truly have to eye-sync things - after this project and the next that I've committed to are finished - I'm going to DUMP all this old equipment and software and either 100% retire or move into the modern world (probably just retire).

Nov 12, 2023 9:02 AM in response to Eve Goldberg

Fixing drift can be hard, especially cutting frames. One way is to try to change the speed of the audio. I can’t remember how easy it is to do in the legacy software. That’s assuming it’s a constant drift and not changing speed during the recording, which can happen with variable frame rate media. It would be good to see the exact information on the clip specs, as it might give an idea what’s causing the problem.

Nov 12, 2023 9:33 AM in response to Tom Wolsky

About the drift: it gets worse and worse the longer the original clip is. That's why I'd eye-sync each clip only after I had a rough cut and have relatively short sections to deal with. (I'd slip the video so it matched the audio in each place, as needed) UGH.


I ran an un-transcoded (raw) clip and it's corresponding transcoded clip in Mediainfo and here's the result:

RAW:

MPEG4

video: AVC

audio: AAC LC

bit rate: variable

video: overall br 8.322 kb/s, 29.970 fps, 1280x720 (16:9)

audio 162kb/sec, 44.1 Hz, 2 chan, AAC LC, Core reader audio


TRANSCODED:

 MPEG-4

video-Pro Rez

audio - PCM

overall bit rate mode - variable

streams:

video - 70.0/mb/sec, 1280x720, 29.970, Pro Rez 422

audio - 44.1 hz, 32 bits, 2 chan, PCM (signed)


Is that helpful?


Nov 12, 2023 11:19 AM in response to Tom Wolsky

Here is the info from the full report:

Raw:

Minimum frame rate: 28.571

Maximum frame rate: 30.00


Pro Rez:

Minimum frame rate: 28.571

Maximum frame rate: 31.579


If changing the audio speed can fix it, do you mean mean selecting the clip in the Timeline and changing audio speed there? I've changed video speed a lot, but never audio speed.


Thanks for all this help, Tom. I appreciate it greatly!!!!

-Eve

Nov 12, 2023 1:25 PM in response to Tom Wolsky

Guess what? Problem solved! Thank you so much. I transcoded in MPEG Streamclip which does allow a fixed frame rate. And the clip plays right in FCP!!! I chose a 45 minute interview clip just to be sure it held. Fantastic! I really appreciate all the time you took to help me, Tom. It will mean a lot for my next couple of months of editing.


BTW: I chose the 29.97 frame rate for the test clip just because I have other footage that doesn't have to be re-transcoded (because it doesn't have meaningful synced audio) that shows up as 29.97 in FCP. Is it a problem to mix 29.97 with 30 if I decided to re-transcode at 30?


Again, THANK YOU!

Nov 12, 2023 1:28 PM in response to Tom Wolsky

Guess what? Problem solved! Thank you so much. I transcoded in MPEG Streamclip which does allow a fixed frame rate. And the clip plays right in FCP!!! I chose a 45 minute interview clip just to be sure it held. Fantastic! I really appreciate all the time you took to help me, Tom. It will mean a lot for my next couple of months of editing.


BTW: I chose the 29.97 frame rate for the test clip just because I have other footage that doesn't have to be re-transcoded (because it doesn't have meaningful synced audio) that shows up as 29.97 in FCP. Is it a problem to mix 29.97 with 30 if I decided to re-transcode at 30?


Thank you!!!!

audio sync drifting

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