Using Avidemux 2.7.1 Release on Windows 10 Pro 64 bit, build 16299.
Attached is MediaInfo output from 3 video files shot with a phone, with the camera oriented at 0, 90, and 180 degrees. Note the "Rotation" field in two of them.
All 3 playback with the correct orientation using VLC and Windows Media Player, but only the 0-degree video displays correctly in Avidemux. Processing with Avidemux and with "Video Output" set to "Copy" strips the rotation/orientation info.
Please make avidemux obey and retain the rotation/orientation field.
Additionally, as a feature request, it would be useful to have a way to rotate a video without reprocessing, i.e. with "Video Output" set to "Copy". Currently the only way I know to do this is to re-encode, and apply a "Rotate" Filter.