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User profile for user: ladedadi
ladedadi Author
User level: Level 1
4 points

iMovie export audio out of sync

Hello,


I've been editing a 1hr video using iMovie. It uses video from two different cameras (one gives .MP4, video files, the other gives .MOV), and audio mostly from a separate recording device (.WAV). I've been lining up the audio to the video manually between edited shots, and it looks like everything is in sync within the iMovie preview playback.


However, when I export it to .mov, under better quality compression, 720p (as this gives 26GB file), I noticed some of the shots are slightly out of sync with the audio, and only in the exported file.


On the 'Get Info' for each type of file, both the .MP4 and the .MOV files say:


Dimensions: 1920 x 1080

Codecs: Linear PCM, H.264

Audio channels: Stereo


Except the .MOV file additionally says 'Timecode' within the Codecs section, and has an additional section saying 'Colour profile: HD (1-1-1)'


The audio recording info says:


Audio channels: Stereo

Sample rate: 44.1kHz

Bits per sample: 16


I've read elsewhere that the difference between 44.1kHz in the audio and 48kHz from the video could cause this problem, but the strange thing is that I'm only seeing this happen with some clips and not others (mostly with the .MP4 clips, and maybe a tiny number of the .MOV clips out of several). The audio has been trimmed here and there in iMovie to cut out small parts, but always lined up manually as close as possible to the video, and as I mentioned there is no noticeable lag anywhere in the iMovie preview, but it only becomes apparent in the exported .MOV file.


Can I ask how should I go about resolving this?


Thanks in advance!

MacBook Pro (2020 and later)

Posted on Feb 19, 2022 7:04 AM

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User profile for user: Rich839
Rich839
User level: Level 8
47,730 points

Posted on Feb 19, 2022 9:17 AM

Combining media from different cameras, and audio with different sample rates, plus different video formats, can cause sync issues. Your original .mov clips can contain different codecs from each other as well. Maybe some have different frame rates as well. The different codecs and formats may render slightly differently when exported. In addition, your iMovie export with best quality (pro res) settings is exporting your original .wav audio as a .mov file with the lpcm audio codec. So you've got a lot going on there.


It is best to have as much uniformity as possible with codecs, formats, and frame rates. You may want to consider converting all of your original clips (or duplicates of them if you want to preserve your original formats) to Mp4/AAC with the free download Handbrake, to impart some uniformity to the various formats. All the clips would be Mp4/AAC. Use the constant frame rate setting. Convert the clips even if the codec already is indicated to be Mp4/AAC. Re-rendering often cures issues.


You can get Handbrake here:


https://handbrake.fr/


A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to complete. Then save and import the converted clip into iMovie and export again. See if that cures the sync issues.


Also, you can try converting you .wav audio clip to AAC or aiff. You can do that by putting the audio clip into a new iMovie project and exporting it with the audio only setting in the iMovie export box, that will give you a drop down menu with codecs to choose from.


Before doing any of the above you might simply try running your present final product through Handbrake and see if that straightens everything out. Also, you could try reimporting your present final product back into a new iMovie project, detach and split the audio as necessary, and correct the sync there.


Finally, you might consider exporting with the Better Quality setting rather than the Best Quality (pro res) setting. Pro res really isn't necessary unless you are doing some intricate professional editing. I doubt that anyone's eye could detect a quality difference unless one zoomed in and examined the pixels. Of course that's your call and largely depends on the use you intend to make of your final product.


-- Rich

.













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User profile for user: Rich839
Rich839
User level: Level 8
47,730 points

Feb 19, 2022 9:17 AM in response to ladedadi

Combining media from different cameras, and audio with different sample rates, plus different video formats, can cause sync issues. Your original .mov clips can contain different codecs from each other as well. Maybe some have different frame rates as well. The different codecs and formats may render slightly differently when exported. In addition, your iMovie export with best quality (pro res) settings is exporting your original .wav audio as a .mov file with the lpcm audio codec. So you've got a lot going on there.


It is best to have as much uniformity as possible with codecs, formats, and frame rates. You may want to consider converting all of your original clips (or duplicates of them if you want to preserve your original formats) to Mp4/AAC with the free download Handbrake, to impart some uniformity to the various formats. All the clips would be Mp4/AAC. Use the constant frame rate setting. Convert the clips even if the codec already is indicated to be Mp4/AAC. Re-rendering often cures issues.


You can get Handbrake here:


https://handbrake.fr/


A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to complete. Then save and import the converted clip into iMovie and export again. See if that cures the sync issues.


Also, you can try converting you .wav audio clip to AAC or aiff. You can do that by putting the audio clip into a new iMovie project and exporting it with the audio only setting in the iMovie export box, that will give you a drop down menu with codecs to choose from.


Before doing any of the above you might simply try running your present final product through Handbrake and see if that straightens everything out. Also, you could try reimporting your present final product back into a new iMovie project, detach and split the audio as necessary, and correct the sync there.


Finally, you might consider exporting with the Better Quality setting rather than the Best Quality (pro res) setting. Pro res really isn't necessary unless you are doing some intricate professional editing. I doubt that anyone's eye could detect a quality difference unless one zoomed in and examined the pixels. Of course that's your call and largely depends on the use you intend to make of your final product.


-- Rich

.













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User profile for user: Rich839
Rich839
User level: Level 8
47,730 points

Mar 1, 2022 11:48 AM in response to ladedadi

That shouldn't be happening. How are you determining the file sizes? What settings are you using in Handbrake? Is it 1080p resolution, same frame rate as original, and Mp4 format, with the Web Optimized box unchecked as it should be? If Web Optimized is checked you will get a smaller file suitable for the Web.



-- Rich


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User profile for user: ladedadi
ladedadi Author
User level: Level 1
4 points

Feb 21, 2022 8:31 AM in response to Rich839

Thanks Rich, that's very helpful! Yes I'll convert all the raw clips in the future before editing. For the one I already edited, I tried converting the entire edited clip using Handbrake but I don't think it made any difference, so I did the next thing you suggested which was to re-import it into iMovie and edited the audio to make it more in sync with the clips.


Thanks again!

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User profile for user: ladedadi
ladedadi Author
User level: Level 1
4 points

Feb 28, 2022 12:30 PM in response to Rich839

Hi again Rich,


I have a quick question about the encoded videos. Prior to encoding, the original MP4 file for one recording was e.g. 4.7GB, but the Handbrake encoded MP4 came out as 357MB, and although it isn't very obviously worse from a normal distance, only upon close inspection does it look slightly fuzzier compared to the original. Is there a way to encode without losing resolution? I didn't change any settings on Handbrake, I just did Open Source, selected the file and then did Start Encoding as per your first message.


Thanks,


Sophia

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User profile for user: Rich839
Rich839
User level: Level 8
47,730 points

Mar 1, 2022 12:26 PM in response to ladedadi

Hmmmm. If you are converting the Best Quality (pro res) PCM file to Mp4, you would get a much smaller file than your oirginal. The .mov pro res file usually is about 4x larger than the Mp4 file. The audio codecs also can affect file size. AAC is fairly well compressed.


If it isn't the above, then I can't account for the smaller file size of the Handbrake conversion.


-- Rich

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iMovie export audio out of sync

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