Capturing a video with working audio on my setup using ffmpeg and lossless recording (the CPU is not fast enough for live transcoding):

ffmpeg -video_size 1024x768 -framerate 25 -f x11grab -thread_queue_size 4096 -i :0.0+0,0 -f pulse -ac 2 -thread_queue_size 4096 -i 0 -c:v libx264rgb -crf 0 -preset ultrafast -color_range 2 Downloads/video.mp4

The result is huge but then I use Handbrake or KDEnlive for transcoding and finalizing the footage.