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Strange increase in size

I imported a 69 minute video in MPEG-4 at 321.6 MB


My task was to trim the video by cutting scenes. I did not add any fancy transitions, and no other modifications.


I managed to trim the video down from 69 minutes to 24 minutes.


When exporting the file with the default settings (resolution: 720p, quality: high), it increased from the original import size of 321.6 MB to 2.29 GB.


How does a decrease in data translate to an increase in file size? I can't make practical use of this without lowering the resolution and quality below the original import.


I found no helpful answers to the similar question previously posed.

MacBook Pro 13″, macOS 11.2

Posted on Aug 17, 2021 11:45 PM

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Posted on Aug 18, 2021 1:39 AM

It is quite simply bit rate.


720p video is normally encoded at around 10Mb per second.


Your original 69 minute video was encoded at a ridiculously low bit rate, probably around 1Mbps which is why the new video is nearly 10 times bigger.


You can reduce the bit rate when you export by selecting Custom in the Quality section and dragging the slider all the way to the left.


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Question marked as Top-ranking reply

Aug 18, 2021 1:39 AM in response to whirledman

It is quite simply bit rate.


720p video is normally encoded at around 10Mb per second.


Your original 69 minute video was encoded at a ridiculously low bit rate, probably around 1Mbps which is why the new video is nearly 10 times bigger.


You can reduce the bit rate when you export by selecting Custom in the Quality section and dragging the slider all the way to the left.


Aug 18, 2021 9:50 AM in response to whirledman

Likely the video that you imported into iMovie was more highly compressed than the video that you exported out, which can account for the larger file size. When a clip is imported into iMovie, iMovie unpacks it for editing. If the imported clip were highly compressed, then when exported out iMovie's compression would likely be much less. Thus larger file size. Less compression usually is a good thing. However, 2.29 GB for a 69 minute video is almost absurdly low. I imagine that the quality is pretty poor.


Other things that contribute to file size are compression settings, resolution, and bit rate.


You can try sharing out to email where you will have small, medium, and large options under the resolution settings, and then dragging the movie out of the email to your desktop.


-- Rich

Strange increase in size

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