iMovie MP4 file space

Discussion in 'Digital Video' started by NDWASI, Oct 12, 2017.

  1. NDWASI macrumors newbie

    Oct 12, 2017
    Granger, IN
    Relatively new to iMovies, I created two MP4 files by editing digital camera home videos using iMovie. I had read that each hour of video translates into about 1GB of storage space as an MP4 file (and possibly up to 2GB per hour if HD). The MP4 files created (50 minutes & 93 minutes in length) both took up hard drive storage space equivalent to an average ratio of 9.1GB/video hour. I have many home videos (most VHS tapes) needing conversion and editing and I am concerned why the large amount of file space for these first two MP4's that I have created? Is there a relationship to the number of edited clips in the MP4 video file (ie. both have a large number with each 3-10 seconds in length)? Looking for a good resource for this question and possible more yet to be encountered.
  2. dwig macrumors 6502

    Jan 4, 2015
    Key West FL
    What you read is inaccurate, incomplete, and/or you didn't read all of what it said.

    MP4 files, like many "movie" formats, are "containers" that can have a wide range of different specs (video format/compression type, video compression amount, audio format, number of channels) far beyond simple video resolution specs. As a result, there is no one size/time ratio.
  3. HobeSoundDarryl macrumors 603


    Feb 8, 2004
    Hobe Sound, FL (20 miles north of Palm Beach)
    There's many possibilities to why so large. The space taken likely reflects how much detail was captured. Maybe those videos have a lot of camera movement? Maybe they have a lot of variety of what is filing the frame and it's changing often? Many possibilities. There is no set formula for how many GB any given amount of video will take. It varies widely.

    The usual solution here is not worry so much about the raw video size. Edit it into a final video like you want (to be able to watch) it, then render it out as a h.264 (or h.265 file if you have an :apple:TV5). In that final form (h.264 or h.265) it will be a much smaller file while still looking great.

    I traditionally imported HD in as Apple ProRes myself. An hour or two there could end up at upwards of 50-150GB in ProRes format. Edit into final form, then render to h.26X. Final file size would be about 10%-15% of the raw ProRes file size. Watch it as a proofing step to be sure it is exactly as I wanted it, then delete the huge ProRes files.
  4. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    Today storage costs about $60 per Terrabyte. so 1 gigabyte costs 6 cents. That huge hour long 9.1GB uses less than $1 of storage. This a WAY cheaper than what you paid for the blank VHS tape. Or to think about it another way a $149 3TB disk will hold about 300 hours of video. So don't worry about the size of the files.

    But you need to edit and organize them. What you find is there is different file formats for processing, archive and distribution. When we import the video we want all the detail we can get. We try to use uncompressed video or if not that the least compressed video. Then after we edit this down to some kind of a product we compress it for distribution. We compress it so that it fits on your device. The device might be a DVD or a file that goes on a phone. Or maybe you keeping in a much higher resolution format for viewing on a TV set. Some format comparable to Blue Ray.

    After we edit the raw footage we have to choose to keep the raw imported data. Will you ever use it again? If you keep it them you have two copies the raw and unedited versions.

    Then you need to think about backup. The rule of thumb is to have at least three copies of the data in at least two different geographical locations. That is really minimal

    So one set one a larger size external disk drive, one set on a Time Machine backup and I'd set a cloud backup service for a recent backup.

    Feel lucky that you are doing this in 2017 when storage is cheap.
  5. kohlson macrumors 6502a

    Apr 23, 2010
    Is the question you're asking that the file size of the final output from your iMovie project is 9 GB/hour? As talked about above, this can get pretty complex. And applications like iMovie don't necessarily create the most efficient file sizes, and some of the file size is configured by the options you choose (or their defaults). I suggest taking one more step. Get Handbrake (which also requires VLC - both free), and have it process your final output. Once installed, its just drag and drop. You will probably be pleasantly surprised at the file size reduction, and no apparent reduction in quality.
  6. Boyd01 macrumors 68040


    Feb 21, 2012
    New Jersey Pine Barrens
    Can you expand on that? Why does Handbrake require VLC? They are both great programs that I use regularly, but I never realized there was any connection. I was using Handbrake for a couple years before I installed VLC. Has something changed?
  7. Unami macrumors 6502a

    Jul 27, 2010
    9.1 gb for 50 minutes is quite high - that'd be about bluray quality for a movie in fullHD. it's all about the bitrate. the higher the bitrate you use for encoding the bigger the file. a mp4 of 50 minutes of anything could also have a few hundred megabytes, only resolution and quality wouldn't be very good (the more bits you use, the more details will be preserved). having said that, 9.1. gb for 50 minutes in fullHD seems a bit much, i'd use something like 10.000 to 20.000kbps - then it'd be below 4 gb, i guess. for 4k content 9.1 gb seems about the right size.

    VHS tapes only have a fraction of the resolution of FullHD (about 1/27) so those files wouldn't need to be as big. just make sure that your project resolution corresponds to the resolution of the material you want to digitize. if imovie doesn't give you enough options, export in a high-bitrate format (e.g. apple prores) first and then use handbrake to make smaller files. you'll probably have to experiment with different presets/settings/bitrates to find the right balance between quality and size for you.

    p.s. there is no relationship between the number of source clips and size of the final output. although, if you have really short clips (below a second, a few frames) and use a long-GOP codec like h.264 (that's what's probably in you .mp4 containers) then they really will get bigger, because the codec would have to create keyframes more often. but in normal use, that won't matter.
  8. kohlson macrumors 6502a

    Apr 23, 2010
    At some point Handbrake started to rely on VLC for its ripping capability. Whatever. Both are free, and Once VLC is downloaded and installed it's transparent to using Handbrake.
  9. HDFan macrumors 6502

    Jun 30, 2007
    In Premiere Pro the default Apple TV Preset for 1080p mp4 VBR 2 pass is 5 Mbps target, with 6 Mbps maximum. That's for a non-interlaced frame size of about ~2 million pixels. There are a variety of ways of calculating VHS frame sizes, but 352 x 576 is sometimes used, giving a single non-interlaced frame size of ~200,000 pixels, almost 10 times less than 1080p.

    So as suggested above take a test file and start doing a conversion at .5 or 1 Mbps. Compare the original with the mp4 version. If you don't like it keep increasing until you find the point at which you get no further improvement in video quality when you increase the bitrate. One hour of 1 Mbps should only take up ~450 MB of disk space. Using a bitrate higher than is needed to capture the data in the original file is just a waste of disk space, unless you're planning to do a lot of editing.

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