Avidemux 4K editing: audio/video sync problem

[Hansenaz]

I'm a complete newbie here. I make simple Youtube videos with an old cell phone and Avidemux editing.

I decided to try making 4K snippets yesterday, and today, when I try to edit the snippets together I see a huge video time lag (video lagging audio). Apparently the video processing can't keep up. BTW viewing the snippets in Media Player there is no problem. Since I never had an issue when shooting 1920x1080 I conclude this is a problem with Avidemux and 4K video and my computer. (Right?)

Is there a nice solution? All I can think of is to maybe downsize all the snippets to HD before editing. I'd rather not (about 100 snippets). I've played a bit with video card setting (automatic, Optimus, Nvidia only) but it doesn't seem to matter.

[Baldrick]

Maybe try Losslesscut to merge/join video.

[Hansenaz]

Thanks for the suggestion. Would this replace Avidemux as the video editor for trimming and joining? Reason I ask is my problem is the trimming - hard to know where to cut when the audio and video are many seconds out of sync. At this point I'm pretty attached to Avidemux.

Anyway I've found an acceptable work around which might help anybody who stumbles onto this thread.

1. I open and append several (say up to 10) raw video snippets (1-10min total) in Avidemux. I want to trim out the "junk" and save what's left into a single file.

2. In the native 2160 line format, the video lags the audio but with these Avidemux changes they sync:
a. Set video output to MPEG4 (x264), and reformat to 1440 (transform-->swsResize 2560,1440)
b. Video--> play filtered (check)
c. Audio-->MP3

3. With this setup, Avidemux syncs aud/vid on my computer as normal and I do simple keyframe trimming.

4. Of course when saving it re-encodes to 1440 but that's acceptable to me (3-8min) and the video quality looks better to me than my usual 1080HD. In practice I can then combine several of these edited snippets into my final YT video, using Avidemux with no further re-encode.