https://www.youtube.com/watch?v=3Vt8WuTZHOk
Need GLFW and OpenGL to compile ds-replay. To build this I used make with MinGW but you can use any other build system.
To record, run the game and log into a character. Set character name and health in settings.txt to match the current ones in-game and run the recorder. The output positions are appended to "positions.txt" file. The format is "[milliseconds since last position],[x],[y],[z]". Coordinates are floating points but written as hex bytes.
Recorder still has bugs! It sometimes fails to continue recording after death and will beep to warn you of that. And I also had two hard crashes during my playthrough when bonfire warping.
To replay, copy "positions.txt" into replayer folder and run it. The controls are WASD QE for movement and arrows/mouse(if enabled) for camera. SPACE/ENTER for play/pause playback. settings.txt has fullscreen/windowed, resolution and other settings.