why is FCPXC using mts file instead of Mov file?

Still struggling a bit with file management in FCPX. I have noticed that if I select Import (and either of the copy otions) Tick Transcode, the original mts file is either copied or left in place and a new ProRes file is created within the library.

BUT the clip showing in the browser and being worked on, is actually the mts file, which seems at odds with what I have been learning in tuorials. I thought the reason you transcoded was to give faster work, better colour etc because your using an optimised file not the original raw file.

Help appreciated please.

If you optimized upon import, then you are actually working in the timeline on an optimized clip. The event browser still shows the original codec of the clip but when you export the timeline you can double check that your source file ( the optimized file) shows as ProRes 422 (or variant). This doesn't seem very clear or intuitive as you might expect the browser to reveal the ProRes verbiage in the codec field.
I am not sure in 10.1.1 version if clips that are already optimal automatically do not get optimized even if you select to do so.

As for part 2 of your question, transcoding is used to provide an editing friendly version of the clip which requires less horsepower to edit with than the original if the original is a highly compressed format such as h.264 or similar. If the program has to decompress on the fly as you scrub through the timeline, performance suffers. By optimizing, your file becomes much larger, remains relatively lossless in quality and processes much more efficiently in your project. It does withstand color grading and layering of effects much better than a highly compressed format does.

Ok so if I am understanding correcty, when I right click on the clip in the browser and click "reveal in finder' it shows me an mts file but the same clip if dragged into the timeline switches to the transcoded file in the library?

I just checked the timline clip that I appended, before I do anything to it. The Video information shows H.264 Linear PCM -- thats not ProRes is it?

The inspector always shows original file information. If there is optimized media available that is always used for playback. The bottom of the info inspector shows the available files, original, optimized, or proxy.

Wow that seems so bizarre - to use one type of file but show the information relating to another type of file. No wonder I am confused.

So as long as I have selected the option of transcoding my original AVCHD file on import I can safely accept that the timeline is using the resultant transcoded ProRes file, is that correct please?

My head hurts!

Yes.

Many of us have complained about the Inspector showing the original file codec, when using Optimized. It is confusing.

Basically, if you import the original to be Managed Media, and Optimize it at the same time, you're wasting drives space, cause FCPX won't use the original at all, only the Optimized. Yes, a very confusing system.

Fill out the feedback form.

Where do I find the feedback form, and thanks all of you for helping to clarify this for me.

In the Final Cut Pro menu.

Thanks Tom done and sent.