Mac OS
Freeware
Handbrake supports 1080p50 and 1080p60 videos, so just convert them to the format supported by iMovie.
Linux (like Ubuntu)
Kdenlive can open 1080p60 and 1080p50 videos. Just create a new custom profile for 1080p60 and/or 1080p50 videos.
Kdenlive performance on a 1080p60 and 1080p50 AVCHD directly is going to be terrible!
There are some alternatives (suggested by Dan Dennedy):
- Transcode your videos to 1080p30 220 Mb/s DNxHD. It is considered "near lossless," and its what AVID systems tend to use. Note that high bitrate can cause cracks/pops/playback issues on the timeline.
Moreovrt DNxHD doesn't support 50/60p so you will always end up with lower framerate.
- Proxy editing by transcoding your clips let's say to standard definition Raw DV or AVI DV and edit them with Kdenlive. Save the project, re-open it with a text editor, replace all ".dv" with ".mts" within the text file and save the project with another name.
Then open this modified project with Kdenlive and render it with your original files using a custom project.
- Transcode raw files with Avidemux to MJPEG (it maintains the framerate) and then import the MJPEG files to Kdenlive on a custom 1080p60 project. Playback, editing and rendering on the timeline is smooth (50/60p).
With options 2 and 3 you can have let's say a final file (MPEG-4/mp4/H.264) still at 50/60p, but edited and eventually compressed.