is there a freeware (software, not online service) that can convert aspect ratio of a video?

Thanks

 

To my knowledge, that's (still) impossible. Cause, If you want a wider frame, where to get the extra visual information from?
A less wide frame is easy to obtain with a crop tool., but then you'll lose pixels.
When 4:3 Television was introduced they already had this problem, so they invented 'Pan & Scan' - they just filmed the Widescreen picture
with a 4:3 camera, so they had to make a selection of what to show and what not, hence the name.

 

Generative AI paint-in!

On a more serious note, you'll have to decide what compromises to make. You can stretch (almost always a really bad idea), crop (bad idea) or you can add black bars (meh idea). Any half decent video converter - even the freeware ones - will let you do all three. You can combine minor amounts of stretching with cropping or minor amounts of stretching with black bars if you absolutely must.

If you only want to modify the aspect ratio, mkv, WebM and mp4 let you losslessly change the "DAR" (display aspect ratio) in the metadata. But understand the implications. All this does is give you a squashed or taller picture.

 

try stretching the video. with video editors

 

Try This

 

press 'A' in VLC

 

xmedia recode <--- by far the best tool for video editing

but it was a little tricky.

 

FFmpeg can do this, but what are you trying to achieve exactly?

https://trac.ffmpeg.org/wiki/Scaling

 

how many millions can you spend?

 

Depending on your file type and what you need to do, the free program MKVTOOLNIX can edit the internal aspect ratio of a video file without recoding the video stream:

https://mkvtoolnix.download/downloads.html#windows

You would click the video stream and scroll down to "video properties", edit the necessary changes then hit "start multiplexing" to rebuild the file.

 

Unless the OP wants to re-encode to adjust the AR this is the best and quickest solution by far.
I also use MKVToolnix because .mkv is the best (and truly free) video container. Well, maybe webm kinda is.

But lately there's been some tools that can do it in mp4 or webm too. Not sure if free tough.

 

do you want to render to a new aspect ratio, or do you just want to view in a different aspect ratio?
VLC will let you change viewing aspect ratio without changing the aspect ratio of the file being viewed.