Lossless Screencast with Audio on Linux

[Habanero2]

Hi,

i want to create a screencast from a video and tried this command line from here https://trac.ffmpeg.org/wiki/Capture/Desktop

ffmpeg -video_size 1920x1080 -framerate 25 -f x11grab -i :0.0+100,200 -f pulse -ac 2 -i default output.mkv

This results in a stuttering video after 30sec and there are a lot of error messages in the terminal window. When i try the command line at the end of the side it works better but its video-only

ffmpeg -video_size 1920x1080 -framerate 25 -f x11grab -i :0.0 -c:v libx264 -crf 0 -preset ultrafast output.mkv

I can't record video and audio together. when i bring audio and video together

ffmpeg -video_size 1920x1080 -framerate 25 -f x11grab -i :0.0 -c:v libx264 -crf 0 -preset ultrafast -f pulse -ac 2 -i default output.mkv

i have the error

Unknown decoder 'libx264'

How can i record lossless video with lossless audio?

EDIT
What is the correct framerate in the command line? my computer is connected to the display with displayport running with 75hz. Do i need to capture with 75fps?

[Blue_MiSfit]

Move the -i default to before -c:v libx264