I would like to speedrun Ace Combat 7, but it's a game so long to complete, the RTA is always over 4 hours, and I haven't the time to do a complete speedrun in one time, so I have to divide it: but if I divide the run is it still valid? (Sorry for my English but I'm Italian)

I think segmented runs are not valid but you can start doing individual level runs. (See here: https://www.speedrun.com/acecombat7/levels )

Ok, thank you, I have an other question: if I speedrun all the mission of AC7 and I rec it by the ps4 rec (so I do a clip video), the clip video have a max duration of 1 hour, so I have to do 4 or 5 rec and I don't think that's valid, so if I recording the tv by the phone camera, is the speedrun valid? considerate that the recording have not good quality. I don't know if I explane it well

Depending on your internet connection you could theoretically live stream from your ps4 to twitch. That would firstly result in a better video quality and secondly give you a recording (past broadcast archive).
If several clips or bad quality recording would be accepted is a question for the moderators (superSANIC).

Ok, and where I can write to superSANIC?

I think it would be easiest to join the speedrun discord server (if you didnt already) ( https://discord.gg/bKJ2sYCu ) and either ask in the #ace-combat-7 channel or message sanic in a private message.

Ok, thank you so much man

Full game runs need to be done in a single sitting.
For quality, I ideally would need to be able to see the mission time in the debriefing screens in order to double check the IGT. If a phone camera is your only option then I guess I could allow it. Just keep in mind that higher ranks = higher scrutiny.

Ok, thank you