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export file size is bigger than the source file

iMovie export file size is larger than the source file.


Source File - 570MB

what I did was trim the last 30 minutes off of 4 hour lecture


Export File (est)

High - 35.93GB

Medium - 24.11GB

Small - 12.28GB

Best(ProRes) - 266.34GB



The source file itself was converted to MP4 from AVI (1.5GB) using handbrake


MacBook Air

Posted on Dec 26, 2020 8:25 AM

Reply
Question marked as Top-ranking reply

Posted on Dec 26, 2020 2:58 PM

Hi,


You get a larger export size than the source because the source file likely

was more highly compressed or lower bitrate than the exported product. Your

source file was 570 mb for a 4 hour lecture, and that is very highly

compressed. From the high, medium, and small export options that you posted you

can see the various file sizes that result when that compression is released

upon export, as determined by your settings.


Things that affect the file size are the codec, the bitrate, the frame rate,

the compression rate, the duration of the movie, the resolution, the complexity

of the edits, and your overall export settings. Faster compression, higher

compression, lower quality, lower resolution = smaller file size. So if you

want to reduce the export size you can tinker with the above items. A lecture

video does not have much motion in it so you wouldn't need the high bitrate,

thus high file size, of pro res. Probably having a lower compression rate

wouldn't matter that much either. You can do a few test exports, experimenting

with the settings, to see what level of quality is satisfactory for your

purposes.


-- Rich


4 replies
Question marked as Top-ranking reply

Dec 26, 2020 2:58 PM in response to The Voice of the Voiceless

Hi,


You get a larger export size than the source because the source file likely

was more highly compressed or lower bitrate than the exported product. Your

source file was 570 mb for a 4 hour lecture, and that is very highly

compressed. From the high, medium, and small export options that you posted you

can see the various file sizes that result when that compression is released

upon export, as determined by your settings.


Things that affect the file size are the codec, the bitrate, the frame rate,

the compression rate, the duration of the movie, the resolution, the complexity

of the edits, and your overall export settings. Faster compression, higher

compression, lower quality, lower resolution = smaller file size. So if you

want to reduce the export size you can tinker with the above items. A lecture

video does not have much motion in it so you wouldn't need the high bitrate,

thus high file size, of pro res. Probably having a lower compression rate

wouldn't matter that much either. You can do a few test exports, experimenting

with the settings, to see what level of quality is satisfactory for your

purposes.


-- Rich


Dec 27, 2020 9:39 AM in response to Rich839

Thank you for your reply, how can I change the bit rate of the video? There are some youtube videos explaining how to manually fine tune the bit rate but those seem to be an older versions of iMovie.


Edit - I found the slider, but is there like a rule of thumb for quality and bit rate ?

even if I lower the slider to the minimum (3.33Mbps) quality the file size is still more than 5GB, even if I reduce the resolution to 720p and lower the slider to 2Mbps (lowest) the file size is 3.7GB. way more than source.

Dec 27, 2020 9:35 AM in response to The Voice of the Voiceless

To be sure we are on the same page, the slider you are referring to is located in the "Quality" option drop down in the share box under the Custom setting.


There really is no rule of thumb other than that the higher the bit rate the larger the file size and the better the quality. It is in the eye of the beholder. Take a small 30 second representative piece of your video and place it in a newly created project. Share it out at various Mbps settings and see what settings give you satisfactory results.


-- Rich

export file size is bigger than the source file

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