Resolved iMovie 9 produces gigantic files on import, fails to generate thumbnails

Discussion in 'Digital Video' started by maverick28, Mar 28, 2017.

  1. maverick28, Mar 28, 2017
    Last edited: Mar 28, 2017

    maverick28 macrumors member

    Mar 14, 2014
    Hello, dear friends, begging for your help,

    I'm recutting a video I made of individual video files 1.5 years ago. All went smoothly then but now it became such a pain and I can't seem to figure out why.
    Software: OS X 10.7.5, iMovie 9.0.9
    Hardware: MacBook Pro, mid-2012 15" non-Retina, 2.3 GHz Core i7, 4 GB RAM, 223 GB free disk space, NVIDIA GeForce GT 650M 512 MB dedicated, Intel HD 4000 integrated
    • MP4 input parameters: H.264, AAC, MPEG-4 ODSM, MPEG-4 SDSM, 15 F/S.
    Using Handbrake I converted a set of MP4 short videos (81 units, ~5 to ~7 min each) to those of M4V format to import to iMovie. The videos of both formats are 15 frames per second (in case the info helps), res. 960 x 600. I left it for a night to do the job but when I returned afterwards I found that while it succeeded importing the files to its Events library (that can be verified by going to the folder where all of 81 imported videos are happily located) it managed to generate thumbnails only for 61 of them.

    I have 223 GB of free disk space. I experimented with importing, unfortunately nothing to pinpoint to exact cause. The only indication that may bear some remote relation is that I can't succeed at accomplishing of getting files of reasonable size on import: I selected "Large - 960 x 584" optimization option, I selected "Full - original size". In both cases it produced insignificant difference of file sizes, 197 and 170 MB respectively, still 10x the average original size. Why? How do I import without iMovie adding extra layers of data? As for thumbnails it's capable of generating them on file-by-file basis and still it takes confusingly large amount of time to import 18, 20 or 30 MB file. So, yes, it falters on batch-importing and thus, fails to generate thumbnails. Conversely, it succeeds at building up thumbnails but produces gargantuan-sized files. Every time I import iMovie estimates overall time left at a very long spans. In my last case these were 5 h "left". I can't recall a simple import taking such a significant amount of hours to complete when iMovie was importing my files 1.5 years ago. In addition, my Mac was running so hot that I feared it could burn off GPU, motherboard, internals also got this UI disorder (see the screenshot) with the progress bar of the upper dropdown window being out of bounds of the main window (or even in other spaces), again, not seen earlier.
    I'm lost. Why does iMovie do this? Is there any option to turn off optimization completely? Any ideas why it misses thumbnails?

    List of pictures attached:
    HandBrake MP4-to-M4V settings (video & picture)
    iMovie graphical mess, displaced progress bar drop down (appearing at different positions on the screen).

    Attached Files:

  2. Unami, Mar 29, 2017
    Last edited: Mar 29, 2017

    Unami macrumors 6502a

    Jul 27, 2010
    first: .mp4 and .m4v are not formats but container - it might depend on the format (e.g. h.264 in your case) whether imovie can handle the files without optimizing. i'm not very knowledgable in imovie, but i suppose what happens here: h.264 usually isn't an editing codec (because it's inter-frame, so it'll small but be very taxing on the hardware) so imovie will probably try to convert it to a more edit-friendly (intra-frame) format like apple intermediate codec or prores so it'll work on slower machines. that's why your filesizes are so "big". but really, 233 gb for more than 400 minutes of video-footage is not very big - when i record in 4k prores, it's about 500gb for just 80 minutes.

    things you could try:
    -if possible, don't "optimize"
    -try converting your footage to 30fps first, imovie might not work with 15fps native footage.
    -use the 30 day trial of fcpx - you don't have to optimize, but things migh be slow, depending on your mac. it should run reasonably on your machine, though.
    -you probably don't need to do the extra step of transcoding the .mp4 before importing, if imovie transcodes anyway. i'm not sure if handbrake transcodes the video or just rewraps it into the .m4v container (if it's pretty fast - a handfull of seconds - then it's probably just rewrapping, if it takes a minute or longer per file it's transcoding - don't do that, you'll lose quality, if you have to transcode use a "bigger" codec like prores 422)
    - in the end you might need a bigger, external harddrive
  3. maverick28 thread starter macrumors member

    Mar 14, 2014
    I don't know what the user Unami had to say but I found the solution.
    The solution was to use the original container, that is, MP4, not M4V! For some unknown, yet to be discovered reason, iMovie resorts to forced optimization of M4V files (even if "optimize" is not selected) in theory identical to MP4 with the exception of DRM regarding management of iTunes content to be played only on iDevices, producing many additional data making for inconveniently large files. So, not so identical. I had fallen back upon M4V because I read that working with this format makes editing more fluid considering very low latency response to movement of cursor. I imported MP4 as is, and it took some 8 (eight!) minutes to process all of 83 files successfully generating thumbnails for all of them. The more detailed account of underlying factors is still a subject of my personal investigation but the fact is crying: do NOT import M4V to iMovie.
  4. Unami, Mar 29, 2017
    Last edited: Mar 29, 2017

    Unami macrumors 6502a

    Jul 27, 2010
    sorry, i might have been a bit confusing (or you might just have seen the quotation of your post that i first posted by accident), but glad you solved it.

    I don't know if that makes more sense, but:

    .mp4 and .m4v are only containers with .m4v also including the apple metadata.
    the file-suffix .mp4 doesn't really say anything about the video codec. in your case it must have been a codec like h.264 that worked with imovie.

    transcoding a .mp4 containing a h.264 video to a .m4v containing a h.264 video doesn't make it more fluid, because it's the same codec. you just lose quality because you're re-encoding your footage once more. it doesn't change the size drastically by itself, though. but maybe by transcoding to h.264 again it was encoded at a higher bitrate, thus resulting in bigger files.

    what does make video more fluid is transcoding to an intraframe codec like apple intermediate or prores. that's what imovie does automatically if it thinks it can't handle smooth playback otherwise. this means that every frame of your video is encoded independently. when editing your mac just has to scroll through that sequence of pictures. that's fast, but as every frame is encoded (like a sequence of .jpgs), this takes a lot of space.

    when using an interframe code like h.264, most frames are saved in relation to other frames. e.g. when the background of your video is static, not much information has to change from frame to frame, so the compression algorithm just saves one full frame and tells the other frames of that sequence to only save the changes that occur over time. that's why h.264 files are so small, but then your mac has to look at other frames first, before being able to draw one, so it's more taxing to the cpu.
  5. maverick28 thread starter macrumors member

    Mar 14, 2014
    Thank you, Unami, you're very knowledgeable and informative. I'll take that into notice for my future projects.

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