did i do any things wrong?

Ah, sorry I forgot your thread. But the good thing is, you posted those details, and I think I spot the problem.


As you can see here, the resolution of the video is 1874 x 1054 pixel, which is a strange one btw, as HD is normally 1920 x 1080 (if 1080p/i).



In here there is the option of "Optimize video", which either lets you select LARGE or FULL. You have selected LARGE. Try it with FULL and then export again


Btw, H264 is not really a good codec when it comes to editing, thus iMovie converts the video to .mov using the Apple Intermediate Codec.

During export the movie is transcoded (converted) to H264 again, which amounts to two conversions, which will result in loss of quality.
But the more important fact is, that your source with 1874 x 1054 pixel gets scaled down to 960 x 540 and then gets scaled up again during export to 1874 x 1054.

I don't know much about iMovie using some kind of proxies, but if I understand it correctly it actually scales down the footage with the LARGE setting. As written before, try it again with the "Optimize video" setting set to FULL.