encoding with x264 and h264 codec only use 30-50% cpu

[jagabo]

1920x1080 uncompreseed YV12 at 30 fps is only about 93 MB/s. So disk I/O shouldn't be a bottleneck on the SSD. Probably not much of one from the hard drive (depending on how old and full it is) either.

[Slind]

1920x1080 uncompreseed YV12 at 30 fps is only about 93 MB/s. So disk I/O shouldn't be a bottleneck on the SSD. Probably not much of one from the hard drive (depending on how old and full it is) either.

about one year old and 60% full + intel software, so this shouldn´t be a problem. If I test it I get about 480 MB/s

[_Al_]

x264 command line works with 100% CPU

so it is perhaps settings, or something in script that Megui creates or some filters Megui uses, you might have checked something in Megui GUI,
I'd double check,
Keep troubleshooting, make your way up, you did easiest video only encoding, now I'd try manually loading Avisynth script directly into Megui

also do not forget about audio, Megui might create something also after loading audio, you mentioned you created that separately, so try video , avisynth script , if you get 100% CPU try to add audio also ....