1080p (4:3) aspect stretched to 16:9 when imported into avidemux

Started by MarkVS, May 08, 2024, 08:09:01 AM

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Sorry to bother with a dumb question:
I have a TV show that I want to edit a couple of things, when I drag the file into avidemux, it's very stretched looking. As if avidemux is seeting it as 16:9 when it's 4:3? This is DURING editing. I understand that I can force aspect to 4:3... but it's ALREADY 4:3.. I just don't understand why it's showing as 16:9 in the actual program. Am I doing something wrong? Thanks


Avidemux always displays videos as coded using square pixels. No stretching / squeezing specified at the VUI (video usability information) or at container metadata level. This is by design, you are not doing anything wrong except for expecting Avidemux to act as a video player.

If the result after editing has wrong proportions when played in a video player, you need either to specify an anamorphic display in muxer configuration ("force display ratio"), specify it (additionally) in encoder configuration when re-encoding or resize the video to square pixels which implies re-encoding (this time without need to do anything with VUI parameters).


Is there any player nowadays which ignores container metadata? I don't think so. IMHO that's the way to go instead of re-coding.



If you don't reencode, then the video plays back with the aspect ratio that the metadata dictates on stand alone, 3rd party players, but not with browsers. There is no problem.  But if you reencode AVIDemux starts by treating the pixels as square.  You can stretch or squash them to whatever is correct, or you can force to set the AR metadata to do whatever you like.  The forced metadata container resize option is a little tricky to find inside the encoding setup and it depends on which video codec you are using.

I have a calculator that lets you reset forced AR in the metadata if you really want to do it at the bottom of this page: https://www.producerelease.com/blu-ray/parcalc.htm#wrapprcalc


Container metadata can be easily edited without touching audio and video inside of container. For instance mkvmerge for mkv container will let you edit most of metadata.



Right, .mkv is a lot easier to adjust Aspect Ratio settings in the metadata. .mp4 is the tricky one.  You stated that you didn't know of a player that ignored metadata.  I assume you mean AR (aspect ratio) settings.

Since web browsers do not playback .mkv, hardly at all, except Safari and older Edge, then anyone playing back the media in a web browser straight has to use .mp4 and the browser will not get aspect ratio adjustments from metadata settings.  Browsers are playing back just square pixels only. 

Since most of the time AR errors are very small, I think most people never notice the problem.  I see it all the time. Perhaps in around 25% of online media archives that are not 16:9 or 4:3.  1.33 is used instead of 1.37 or 1.66.  2.37 is used instead of 2.35 or 2.39.  1.78 is used instead of 1.85.  All these can easily be missed.  Most people would not notice.

All can be fixed with AVIDemux.  Crop out any black bars and check the remaining AR with a size adjustment filter and compare it to the listed AR for the media online, available with a membership imdb account.  It's wrong very often.