For editing the resulting raw video, you can use (VideoPad)[https://www.nchsoftware.com/videopad/index.html]. It is quite powerful and is free for non-commercial private use. It has some annoying popups though and will not allow you to export videos as MP4s and FLVs though...
Video editors can normally detach an audio track and then you can record or insert another on a separate audio track. Then reencode the movie.
As for the h.264, just sent your reencoding to the one you want and highest quality. But it probably won't keep it as good as the original.
VideoPad comes to mind. It may still be free, at least for a trial.
I've had success with Camtasia (mostly for recording training videos) in the past.
Over the last year, I've been using NCH Video Pad editor and am really happy with it.
VideoPad is very format-agnostic and therefore also supports popular open source standards like WebM and Matroska (with VP9 or H.264 video but for some inexplicable reason H.265 is only supported in the MP4 container and not in other containers that also supports this codec).
The free version works for the most basic tasks, but you would probably prefer to spend 40$ / 35€ on the fully-functional Home edition. It comes with plenty of filters, and I would say it qualifies as a fully-fledged non-linear video editing tool. The bonus is that it also supports lossless editing (sequential cutting) with remuxing options.
I have to stress that I haven't really tested it myself, but several people have recommended it to me.
You can pretty much use most video editing programs out there for that. I personally used the VideoPad Video Editor by NCH to look at an ARG video a while back since there's a free trial edition of it which had stuff like brightness and contrast adjustment and frame by frame skip built in.
I worked for six hours trying to make this borderline shitpost, The Music is by a gread Lad called Vox Caster and the song is called Why do I still live? I used bootled tier photo editing software and a video editing software called VideoPad. If this gets enough atttention I may make something else like it.
I suggest VideoPad, on the main page you can find the paid version, but if you specifically search for it on google you can find a link for the free version usable for non-commercial purposes.
It's fast, lightweight (15mb installed), user-friendly, it opens in just a second and it has 5 export presets that allow to easily maintain the quality high and the size small. It's my go to for removing useless parts in my university lessons I recorded.
I use VideoPad Video Editor here.
It's free. Has a bit of a glitch here and there, like matching audio speed adjustments over longer periods of time, but it works.
Hey there Bimmelhex - I actually just learned how to do this for the 'ballad of the vitards'. I used the NCH "VideoPad Video Editor" which is free. It works OK, YouTube has some decent tutorials using it. Others probably have more insight (mikeymike??)
I'll try posting the link below, I live in the U.S. so don't know if that makes a difference for you:
Video Editing Software. Free Download. Easy Movie Editor. (nchsoftware.com)
Cualquier simple editor de video lo hace.
Si solo queres hacer eso, descargate el editor VideoPad Editor, pesa muy poco y es simple. (Tenes un tiempo para usarlo libre, después te pide pagar licencia, pero es fácilmente pirateable buscando una licencia en google).
https://www.nchsoftware.com/videopad/index.html
VideoPad... it's free and pretty easy to use.
A lot of effects are made difficult without the many presets, etc. that paid programs have, but most can be achieved with a bit of digital elbow grease.
Plus, if you just want to put clips together and throw music over it, any editor works really. I'd suggestion googling a list of free video editors, downloading a few, and deciding which one works for you the best, but I personally use VideoPad.
I use VideoPad Professional by NCHSoftware for both making my videos and for opening up the video footage as stills and pulling out images frame by frame to make all the screenshot images that I use to illustrate my how-to articles.
It was $50 when I bought it, and that was a sale price. I think it was $70 full price. But I bought it years ago (around 2014, I think) and I think the price for the latest edition is quite a bit more. They had a home edition that had fewer features and a student edition that was a lot cheaper but couldn't be used for things like YouTube and Twitch. Don't know if they still offer those editions any more or not.
It is very similar to Sony Vegas, does most all the same things, but "looks old" and is $500 cheaper.
They used to offer a free to try version that you could use for 30 days, and then it expired, but I don't know if they still do that.
EDITED TO ADD:
I just checked their website ( https://www.nchsoftware.com/videopad/index.html ) it looks like they don't make the one I have any more (logical, seeing how I bought it so many years ago) and replaced it with one called VideoPad Master's Edition, which appears to be the same one I use but now with more features. It says it's $99 now.
We understand what you're after. But trust me, applying such a distortion to a video is not going to give you the effect you think it will.
You are much better off just playing the 2D video in a VR movie player that allows you to alter the position and size of the virtual screen.
If you really want to go ahead though, you can try the "Place in 360" video effect in an application like this one.
Be aware however the resolution of your output video (as a guess) is going to need to be like 8 times larger than it is already just to account for all the blank background space if you want to maintain about the same visual quality. Whereas in a VR media player, you'll lose nothing (basically).
On of my most underestimated tools is ShareX for creating GIFs. If size is an issue, I sometimes also use GiffingTool. And VideoPad for cutting that sweet trailer for your game (not free, but the perfect balance between ease of use and features).