I have a relatively small video of a screen recording of about 600kB in H.264 / VBR. Now I wanted to edit some unnecessary parts out. So I edited the clip and exported it, just to discover the size balloons up to 18MB. I used the "Share" button on the top left and an Apple Device 1080p preset.

The result is the same, for iMovie or FCP.

Is there an export method that preserves my original small video size or let me encode in VBR?


When you click on the share button you will see “Add Destination “. In the window, you see all the possible export formats. Formats with “Small” or SD will make the export file size smaller. Try MPEG if your device can play it. However, with small file sizes, your tradeoff is low video quality in most cases.

  • How does SD/Small preserve my original size? I do not want to size it down. The problem is that the file size increases, despite being the same resolution as the source material.
    – Era
    Jul 29 '19 at 20:07
  • Exporting will use different codecs wrapped in a container file. Depending on what you choose for a codec, this will mean different file sizes as a result. If you don't have an editing software which natively supports the codec from your original file you will always have differences in file size. Jul 29 '19 at 20:16
  • I assume your original footage was already automatically transcoded from FCPX to make it compatable for editing. Jul 29 '19 at 20:19
  • My original footage is a 600kB MP4, and I export it to a 5.4MB MP4 using Compressor. I can't even get the file size down to original if I manually reduce the bitrate.
    – Era
    Jul 29 '19 at 20:29
  • MP4 is the container file, However the inside can be may things, hence the diffence in file size. Jul 29 '19 at 20:34

I ditched FCP/Compressor altogether. Using ffmpeg I converted the FCP output filesize down by a factor of 10 without losing quality.

ffmpeg -i in.mp4 -vcodec libx264 -f mp4 -b:v 1024k -an -crf 20 -preset veryslow out.mp4

Quite honestly, it is a joke that a 330 USD software cannot encode H.264 with VBR.

  • Variable Bitrate (VBR) allows ProRes to be economical with video storage, without damaging the visuals. This type of damage will sometimes occur when max bitrate is exceeded with codecs that are fixed. So for instance, if we encode an action sequence, ProRes can use a higher data rate which will ensure that image loss is negated and the detail of the video remains. Then say, we have a simple two-shot dialogue sequence. ProRes reallocates only the bitrate needed. ...(premiumbeat.com/blog/5-things-you-should-know-about-prores) Jul 31 '19 at 19:15
  • Thanks for another pointless quote. What does ProRes or anything you just said have to do with any of this? I know how CBR and VBR works. So what do you want to tell me here? I already regret asking any questions on this site, since it is perfectly obvious by now that nobody here has a clue what they are doing. Just some children playing with video software...
    – Era
    Aug 1 '19 at 21:21
  • This comment was to inform others that in fact, FCPX is capable of VBR with H264 when using ProRes. Aug 3 '19 at 6:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.