Modify aspect ratio without re-encoding (x264)

[MindBlank]

I have a bunch of x264 encoded files (.avi) that have the wrong aspect ratio : they're 16:10 when they're supposed to be 15:9.
I want to change the aspect ratio but I don't want to re-encode them as I'll lose quality and it would take days.

So far, I've used on other x264 videos a little program called H264 Aspect Ratio Modifier(modified them form 16:9 to 16:10), but it can only modify predefined AR's to other predefined AR's and custom ones to other custom ones, so it doesn't let me do anything, as 16:10 is predefined but what I want (15:9) is not.

Do you guys have any idea how I can do this without re-encoding? It would be a very big help if I were able to do this...

[Baldrick]

With MPEG4Modifier can you set a custom aspect ratio.

[poisondeathray]

you can set it in the container level as well e.g. mkvtoolnix

or change SAR in the bitstream with an experimental ffmpeg version
http://forum.doom9.org/showthread.php?t=152419

(note SAR in AVC terminology is the same as PAR in conventional terminology, so you have to figure out the correct ratio)

[MindBlank]

Baldrick, it seems that MPEG4Modifier doesn't support H264, so I couldn't do anything with it.


poisondeathray, I'm going to have a look at that link, but it seems kind of complicated, I might need help (have a few questions...).

[poisondeathray]

The easiest way is to set the DAR in mkvtoolnix

[MindBlank]

Hahaha, awesome little tool... (I mean the ffmpeg one)

I knew about its existence but was wary of trying it due to being command line based. Just awesome.

Yeah, I had to figure out the correct ratio (25:24 in my case) and it worked perfectly.

Thanks (again ) for your help poisondeathray.