Edit small portion of a compressed video without losing quality I have a one hour h264-encoded video. The unedited footage can't be found.
My goal is to edit a small portion of it.

The scenario looks like this. I have to blur out some persons appearing let's say:  00:20:00 - 00:22:00.
The Video's between 00:00:00 - 00:20:00 and 00:22:01 - 01:00:00 are untouched.

Is there a method achieving this without losing quality on unedited footage?

I'm using Adobe Products.
For tasks like this I like the TMPGEnc tools, try Smart Renderer https://tmpgenc.pegasys-inc.com/en/product/tmsr5.html.

With these tools you can cut &amp; join files, only re-encoding where the cuts / joins are. I would split the file in 3, preferably on key frames, re-render the edited section as needed, then re-join the files. There are trial versions of the products, just download it and see if it does what you need.

I don't know of a way to do this in the Adobe products - if anyone else does, let us know! Or possibly there are other free tools to perform this task, I've just always used the TMPGEnc tools for this type of work.