[Rx] How to Trim MP4 Videos


Ever been sloppy and left a bunch of junk at the beginning of a screen recording figuring to trim it up later?  Easy, just grab a free MP4 trimming tool and clean it up, right? Ah… no.

How to Trim Mp4 Videos

Problem: It turns out that trimming a mp4 screen capture/video is not trivial. Most of the standard video formats are lossy and the compression algorithms use information from previous frames. If you delete the key frame, a part of your video will go goofy.

Solution: Avoid the problem in the first place and make the screen capture as good as you can. Otherwise, if you need some trimming, do the cuts and re-render the video. Note that the re-rendered videos are probably going to be bigger than the original. As for re-rendering, the open source, free video editor Shotcut did a better re-rendering job than my old Movie Vegas Studio video editor.

WARNING: Beware of software that says free and easy. Some “freeware” bundled
with crapware zapped some of my audio codecs. My little trimming task ended up taking a
half day to fix.

Searching for the Mythical Lossless MP4 Trimming

A good number of the free software websites lead to infomercials for Wondershare’s Filmora, which watermarks the video and isn’t exactly “free.” I tried most of them. For lossless free mp4 trimmers (all key frame dependent, so your mileage may vary), these two are the best and worst of the lot:

Avidemux 2.6.13Avidemux


  • Active Open Source
  • Simple Interface


  • Audio defaults to Dummy (no audio)
  • No audio cue bar to help trimming
  • Sometimes buggy

Avidemux works okay as a MP4 lossless trimmer if you’re lucky enough to have the key frame in the right place.

The audio output defaults to “dummy.” If you don’t have any sound, check:

Edit > Preference > Audio Tab > Audio Device: Win32.


“Free” Video Editor
(not recommended)


  • Looks like the PERFECT solution


  • Installs 3rd Party crapware
  • No original lossless format without buying a “Premium Membership”
  • WORST. Large promises with little delivery.

This software has the best looking interface of the lot and and it is recommended on a few review sites. BUT besides trying to install a ton of crapware 3rd party bundles, the latest version is a real turd doesn’t allow you to save in the original lossless format without buying a “Premium Membership.” The forum suggests that even the premium membership version doesn’t add anything new. 

Previous Version. It seems like the previous version (still floating around) had the crapware, but was a much better program. In any case, this older version attempts to installs the PUP (Potentially Unwanted Program) OpenCandy that might be flagged by your anti-virus (although it’s not technically a virus).