I mean... if you can see this, can you comment on it?
It looks like your previous submissions were made "dead" automatically.
My guess is this happened automatically from the combination of Youtube video as source and "Show HN" in the title.
"Show HN" is for things you have made yourself. But only when there is something other people can "play with or try out." Show HN isn't for passive content. Regular submissions are for showing passive content to HN...submitting a link will show HN (of course, HN may not show interest).
I looked at the videos and they would be fine as ordinary links. And if you made them yourself, the "Show HN" is not entirely unreasonable, but not how the community expects it to be used.
Hope that helps.
[edit: reposting the same video on the same day as a first post from a new account probably didn't help with the automatic algorithms that make things dead]
[edit: I vouched for the two videos..."vouching" has a karma threshold. I don't know what the threshold is. They no longer show as "dead" on my computer.]
[edit: turning on "Showdead" in your profile will show you comments and stories that have been made dead. Not sure if there is a karma threshold. But otherwise dead comments and stories don't appear in your feed]
You have now 26 karma and you could submit a question, so I assume there's either no minimum karma or it's very low. However, I wouldn't be surprised if the submitter's karma plays a role in the ranking or flagging logic (they might pay more attention to flame or spam topics for new accounts).
There's this repo that documents other things, though not what you asked, I'm not sure if it's still correct https://github.com/minimaxir/hacker-news-undocumented