Many suggestions of improvement

[Selur]

Alright now the "auto" box is disabled, but the color space is still on 4.4.4 as soon as I check the "lossless" box. So if I import, let's say a 4.2.2 video, it'll encode it in 4.4.4 if I don't change manually the color space. Wouldn't it be better to retrieve the input source color space ?

Not to me. Personally, I only use lossless encoding as an intermediate (or archival format).
As intermediate format, my target normally is not the same as the input, since I did apply some filtering and want to keep as many details of the stuff I did as possible. Also, I usually encode everything at 10bit to avoid banding and have better compression.
Archival is usually the same, I did some filtering to a source I want to archive a specific state for a later time.
If I wanted to archive the original, I would stick with a copy of the source.

When capturing something to a lossless format, I would stick to the original color sampling and bit depth to avoid stress and problems during capturing.
As soon as I filter the source and go for lossless, it does not make sense to me.

The only reason I can think of atm., is if I wanted to feed another program which only supports specific color samplings.
(As a side note: I usually would not use H.264 lossless since most hardware decoders won't support it.

But as soon as the output color space is different, many pixel have different saturation/luminosity.

okay.

Cu Selur