Why does exporting a MOV file in QuickTime reduce file size so much?

Discussion in 'Digital Video' started by camner, Jun 28, 2015.

  1. camner macrumors regular

    Jun 19, 2009
    There is clearly something I do not understand about digital video...

    A 3 minute movie taken on my Canon G15 camera runs about 600MB and is stored in .MOV format. I can open it in QuickTime Player, of course. When I go to export it, the highest resolution export option is 1080p, and when I export it in that format, the file size shrinks to about 75MB, but it stays in .MOV format.

    Clearly, information is being thrown away, though I can't see a degradation in quality on a MB Pro screen.

    Is the original a much higher quality copy and should therefore be kept for archival purposes? How do I determine the quality difference (other than via the file sizes) between that original and the 1080p version?
  2. e1me5 macrumors 6502


    Jun 11, 2013
    Qt compresses the video with a lower bitrate than the original. It is optimized and only useful for uploading on the web or to send it to a mobile device for playback. If you plan to use the footage later to edit it, it is better to keep the original one as it has more information to play with.
  3. kohlson macrumors 68000

    Apr 23, 2010
    You mean QTX, right? In general, QTX tries to put a more user friendly face on the complexity that is video, and makes makes good "guesses" about things like bit rates and compression levels. 80% reduction is pretty good. To see the difference in bit rates, select the files and do Cmd+I and see the info. Video files have lots of variables, and the art/science is getting the best quality in the smallest file for the target consumption platform/viewer. Regarding whether you should keep the bigger or smaller file - most people run out of storage room. But disks are cheap.
  4. camner thread starter macrumors regular

    Jun 19, 2009
    Thanks both for your replies. I did mean QT Player. I didn't realize this until recently, but QT Player does allow exporting in various formats and sizes (it also will rotate a video).

    Another question, if I may...

    .MOV files directly off the camera seem to be particularly large. If I use Handbrake (with the right settings, though I don't know exactly what they are!) I can convert to .m4v and use H.264 to reduce the file size somewhat. Is that, too, significantly degrading the quality? I'm looking for what is a reasonable way to store files long term (for possible reuse).

    These videos are not things that will be made into the Great American Movie, they are just family videos of the grandkids that someone may someday want to turn into something beyond "upload to iCloud so that the rest of the family can see" (which clearly doesn't need a high bit rate and resolution).

    I'm obviously pretty new to video...I'm trying to avoid the mistake I made early on with images where I worked one a jpeg image and repeatedly saved it, of course suffering significant degradation in the process, not knowing that each time I did that I was recompressing the data and thus throwing away much more than I then understood.
  5. kohlson macrumors 68000

    Apr 23, 2010
    Your Handbrake scenario may be misleading you. Handbrake reduces the file size by adjusting the compression to fit a target consumption profile. While this can be done with a different codec, it's in all likelihood adjusting the parameters f the h264 codec that's already in your .mov/m4v container (aka file). See

    In general, the smaller the file the less the quality. But whether the target environment can discern this difference is the key.
    The files are large when they come out of your camera because you can always make them smaller (reduce detail/size/quality), but you can't really do the opposite. So think of the large file as the master, from which you can make different/smaller files. The concept is the same in jpg and photocopies. The closer you are to the original, the better the quality will be.
  6. Small White Car macrumors G4

    Small White Car

    Aug 29, 2006
    Washington DC
    This is your confusion. There is no such thing as an "MOV format" video.

    Quicktime is just a container. You could store SD h.264 in it, HD AVCD, or 12 bit 4k RAW video in it. Or a million other things. They would all be .MOV files if saved as a Quicktime file and yet they'd have no similarity other than that.

    It all comes down to how your application is saving it and if it gives you any options or not. "Apple Compressor" on the app store is one of the more inexpensive options that gives you many options. Handbrake has fewer choices but is free. Something like the Quicktime player narrows your choices down even further, it looks like.

    To answer you original question, open each file in the Quicktime player and hit command-i while you're looking at it. It will tell you what the format and bit rate of each video is. We could help you interpret what you find.

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5 June 28, 2015