Cannot Set Markers or Edit MP4

[frame0]

I'm a new user and attempting to learn the UI and tools by editing a short MP4 video recorded with Zoom that is 2.8 minutes in length.

I am using the 2.7.6 EXE version from the main Avidemux site.

I am only able to set the A marker at the position shown in the screen shot which is not reflected in the A marker setting.
There is no response when I try to set the B marker

Video-Audio Outputs = Copy
Output format = MP4 Muxer

[eumagga0x2a]

First of all, please use the latest 2.7.7 nightly build for overall better experience (major bugs in cut point check code fixed, some color conversion issues and color range handling fixed, other improvements under the hood).

https://avidemux.org/nightly/win64/ (MinGW builds)
https://avidemux.org/nightly/vsWin64/ (VC++ builds)

If you want to edit in copy mode as suggested by "video output" setting, then you are restricted to keyframes for usable cut points. Seeking by dragging the navigation slider or by up and down arrows seeks to keyframes only. It is totally possible that the keyframe at 00:00:02.800 is the only (or the only other) keyframe in this short video. To set marker B to another frame, you need to navigate to that frame, e.g. by playing the video, then stopping shortly before the right spot, then using the right arrow key to step frame-by-frame until you find the right one, then set the marker.

Stepping backward is also possible (the left arrow key), but is orders of magnitude slower.

If you want to set the end of the selection to the end of the video, use the corresponding function (with alternative keyboard shortcuts enabled in Avidemux preferences, press "E") to navigate to the last frame first. Alternatively, just reset the markers ("R") without moving away from the marker A position, then set the marker A again.

[frame0]

Thanks very much; is there an alternative to editing in copy mode?

[eumagga0x2a]

The alternative to copy mode is re-encoding mode. If the video needs to be re-encoded (e.g. because you want to apply filters), cuts can be placed at any type of frames.

[frame0]

Is there a loss in quality?

[eumagga0x2a]

It depends on the chosen codec and codec settings. As a rule for all lossy codecs: yes, there is.