Split-second Pixellation "Flash" When Exporting Short Video from iMovie

Question

Split-second Pixellation "Flash" When Exporting Short Video from iMovie

Hi -

I created three short videos, each less than 7 minutes, shot on my iPhone 7. None of the clips are pixellated when I import them from my iPhone into iMovie (connected directly because my Photos didn't import them all.)

In two of the three videos, I get a short "flash" of pixellation when they export (less than one second - maybe .2-.4 of a second), in each video at second :50. Not sure if this is a coincidence. I'm not using the same clips for the videos - all different.

Further, when I play the videos back in iMovie, sometimes they pixellate for this same split second, and sometimes they don't. Mostly they don't. Both, when they do, show a pixellated image of a frame which appears to be from the first clip. Each of these videos only have a few clips.

The third video came out fine, shot in the same session as the rest, with the same settings.

Can anyone help me with this? I'm a total luddite when it comes to video production, and I don't have any other moviemaking apps or software (even if I did I wouldn't know how to use them.) I hope there's a simple solution!

Thank you,

Kristen

MacBook Pro 13”, macOS 10.15

Posted on Feb 3, 2020 8:50 AM

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Answer 1

Best reply

Rich839

Level 8

47,268 points

Feb 4, 2020 8:45 AM in response to KristenCouchot

You might be experiencing the artifacts/pixelation that others have reported. There may be a correlation with videos taken with newer iPhones and/or the HEVC format on iPhones. So far I have not seen a true solution. As a workaround, converting the video clips to H.264, Mp4/AAC sometimes cures it. You can use the free download, Handbrake, to do the conversion. Here's the link for the Handbrake download:

https://handbrake.fr/

Also, take a look at this rather long thread and see if anything in there helps you:

https://discussions.apple.com/thread/250751600

-- Rich

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Answer 2

Mar 7, 2020 1:24 AM in response to KristenCouchot

I believe I found a solution that works. I was getting badly pixelated artifacts semi-randomly in my video when I would export to MP4 in any resolution. I was using video clips shot on an iPhone 8.

To resolve it, I rendered my heavily edited project to a 1080 Pro Res (.mov) file, which essentially flattened the timeline to a single video clip and did not have the artifacts created by the MP4 converter (I believe). I then created a new project and imported the .mov file I just produced. Once I added that to the new timeline, I am able to export it to any MP4 resolution with no artifacts. I've done this about a dozen times now with the same result - no more glitches/pixelated frames or transitions.

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Answer 3

Feb 5, 2020 12:03 PM in response to Rich839

UPDATE: I tried Handbrake and it didn't help at all. Exactly the same issues in the movie.

So, I decided I would cut out the offending section. However, when I made the splice right before the artifact, I noticed it didn't appear in iMovie anymore. So, without doing anything but splitting the clip immediately before the artifact (and not adding in any transition - just the split), I exported the movie, and VOILA! No pixellation! HOORAY!

No idea why this worked, but there you go. It worked for both videos.

Hope this can help others :)

Kristen

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Answer 4

Rich839

Level 8

47,268 points

Feb 5, 2020 12:56 PM in response to KristenCouchot

That's great, Kristen. Glad it's working for you.

In your case you apparently had some actual corruption in the clip that caused the pixelation. When you cut it out that solved the problem.

Perhaps what you were experiencing was not the same cause as others have experienced. Others have tried your solution without success. So you'll need to work with the project for awhile to determine whether clipping out the artifact actually is a permanent solution. Hopefully it is permanently solved.

-- Rich

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Answer 5

Feb 5, 2020 1:17 PM in response to KristenCouchot

Hey Rich - let me clarify - I did NOT cut anything out - just split the clips. At least 1 second prior to the artifact appearing. I didn't have to remove anything - the movie appeared exactly the same since I didn’t add a transition between the newly created two clips.

k

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