A few of the books I have been reading about using an NLE, Premiere and such, mention YUV and RGB timelines.

Is this something I should consider in kdenlive?

I have a Canon 5D mkII, h264AVC YUV I think? So if I want to output to say a BluRay compatible or maybe DVD format, does is whole process in kdenlive YUV.

I read of being careful not to use RGB effects with YUV as it spoils quality?

no
yes
depends on your level of expectation and satisfaction. Most effects in MLT are YUV except frei0r, which are all RGB.

Ok, thank you, but still a little confused.

If I can do YUV straight through, but Frei0r are RGB, then I should perhaps not use Frei0r? or more accurately as you say, if I find something happens to the quality I don't like coming from what is a decent camera. I'd like to maintain quality as best I can, but perhaps no doubt quality drops with editting and effects and such.

If I use Frei0r plugins, could you explain a little what happens, do they convert the YUV frames the effect is applied to, to RGB and back? That's the confusing bit.

I did a bit more research as the thread didn't get an answer for sometime, Frei0r seemed to offer both RGB and YUV but perhaps not?

I'm a bit ignorant to what MLT offers as effects, could you mention them or point me to the documentation/help files?

YUV was invented for data compression by subsampling the UV chroma channels, this trick dates back to the 1950s color TV research.

So RGB is usually superior, and an YUV -> RGB -> YUV conversion can be lossless, if done right.

Yeah, Marko is correct that RGB space contains more information. MLT prefers YUV processing mainly for speed. I can not entirely backup the claim that the conversion is 100% lossless. If we research this, we may find contradictory information. And the about facts "if done right" are probably not completely congruent.

Anyways, I think all MLT effects are not RGB except burningtv. Some of them are dual mode because MLT does lazy conversion between colorspaces. It keeps the current colorspace until something else is needed through image processing steps. The "until something else" part is based on whether an effect requires a specific colorspace or not, and most of them do (only a small subset is dual mode).

As for frei0r taking YUV, that might be in the API, but I do not think any of them do, and MLT only uses RGB with frei0r. You can get a lot of frei0r effects at the command line:

$ melt -query filters
$ melt -query transitions

All beginning with "frei0r." are from frei0r.

Thank you both very much, that does make more sense now.