Videos encoded by Avidemux have lower quality than videos encoded by the HandBrake app.
Even videos encoded with the Huffyuv codec have lower quality than videos encoded by the HandBrake app.
Is there a way to improve the quality of videos encoded by Avidemux?
Make sure that in Edit / Preferences / Post-Processing all the checkboxes are unchecked.
Also, the latest version of Avidemux (2.8.2) is available below. The settings szlldm mentioned should be disabled by default if using a current version.
https://www.avidemux.org/nightly/win64
The problem is that while post-processing defaults to off, Avidemux respects whatever setting is stored in the Avidemux profile, thus obsolete legacy versions keep to screw up users of current developer builds. Will rename the relevant preferences to set an end to that.