Ffmpeg – Changing frame rate without re-encoding

I am trying to change the framerate of a video so it runs a little longer. I don’t want to re-encode and I want the audio to remain in sync. I was able to extract the raw video from the video and then remux using…

ffmpeg -i source.mkv -c copy -f h264 video.h264
ffmpeg -r 23.976 -i video.h264 -c copy dest.mp4

This creates a video that now runs the correct time with no audio.

How can I get a finished .mp4 with the audio?