High quality screen capture with Ffmpeg

Capture without audio:

ffmpeg -f x11grab -r 25 -s 1280x720 -i :0.0+0,48 -vcodec libx264 -vpre lossless_ultrafast -threads 0 video.mkv

Compress and convert to MP4 format (Youtube ready):

ffmpeg -i video.mkv -vcodec libx264 -vpre hq -crf 22 -threads 0 video.mp4

Lower -crf gives higher quality.

For including audio see refs.