How is Photos able to reduce video files sizes so much on export?

i realize digital photography forum, question result of using photos, if posted in wrong place let me know , i'll delete , move it.

ditched use of camcorder taking video , using sony digital camera still picture , video capture needs. when plug camera imac , open photos imports both still pictures , video files, have video files in photos.

@ first thought problem assumed video files should go imovie. after using photos export video other purposes i'm seeing photos able reduce file sizes of exported content.

so, feel different video formats (mp4 , avchd) , ensuing file sizes decided try simple unscientific test. here's did step step.

1) using sony rx100m3 digital camera took 10 seconds of same scene of video (video indoors of kitchen table) using 4 different video modes. 4 modes , files sizes after being imported photos are:

mode - file size in photos after importing camera
mp4 1440x1080 - 16.8mb
avchd 24p 17m(fs) - 21.4mb
avchd 24p 24m(fx) - 28.5mb
avchd 60p 28m(ps) - 34.4mb

note: avchd files in photos imported .mov , 1920x1080 , h.264. what's odd mp4 file camera says 1440x1080 shows in photos 1920x1080, i'm not sure how works resolution changes 1440 1920 going camera photos. if know here, please chime in , answer.

2) plugged camera imac , imported 4 video clips photos

3) exported 4 video clips using 1080p video quality option. below new exported files sizes , % reduction.

mode - original & new file size after export @ 1080p - % reduction
mp4 1440x1080 - 16.8mb , same after - no reduction
avchd 24p 17m(fh) - orig 21.4mb , new 13.6mb - 36% reduction
avchd 24p 24m(fx) - orig 28.5mb , new 13.5mb - 53% reduction
avchd 60p 28m(ps) - orig 34.4mb , new 22.8mb - 34% reduction

know in detail photos doing these significant improvements (reductions) in video file size? in particular, 24m(fx) reduced more half. oddity how fx reduced +50% while fh , ps in mid 30% makes fx file size same fh.

said, when playing/watching them cannot tell difference between of these files (they great), yet sizes smaller. note: done on 2011 mbp on yosemite 10.10.3 , photos 1.0. doing makes me think should export video files out of photos @ 1080p , them import them in save hard drive space. thoughts anyone?

lastly, (like was) curious exported these files using 720p option see how reduce size , here results. , in opinion 720p looks great on hdtv screen.

mode - original & new file size after export @ 720p - % reduction
mp4 1440x1080 - 16.8mb , new 10.6mb - 37% reduction
avchd 24p 17m(fh) - orig 21.4mb , new 9.5mb - 56% reduction
avchd 24p 24m(fx) - orig 28.5mb , new 9.5mb - 67% reduction
avchd 60p 28m(ps) - orig 34.4mb , new 16.2mb - 53% reduction

well, that's it. , forward hearing others going on behind scenes here.

 

i'd imagine compressing it, resulting footage lower bitrate not enough notice obvious differences.

if can't tell between 2, , disk space hard come by, i'd go ahead , convert lot!

mind if plan on editing in imovie, higher bitrate footage easier manipulate/colour correct due retained detail in shadows , highlights etc.

 

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