Just download Half-Life 2 from Steam or you can download Source Unpack from Resources (Don't use it, if you're going to do RLD skip) To submit run you only need a video
press the button next to "Game Time and Auto Splitting are available (by fatalis)" that says "Activate" to get the auto splitter. For cut scene skips, there are a variety. I'd recommend watching waezone's tutorials, he has 2 live tutorials
and he is currently making a more up to date tutorial series https://www.youtube.com/playlist?list=PL84A17W6AtxVTZ7aErwsj94UOjwqqj_m-
these should give you most of the information you need, and the rest of his channel has some in depth tutorials on Red letter day skip, breenblast yesclip, and more.
Starting today, the custom-made build of Half-Life 2 known as "Ghosting Mod" will no longer be used as a valid build for speedrun.com run submissions, as was determined by a community vote held in the SourceRuns Discord server.
If you are currently using Ghosting Mod to submit your runs, we ask
