PS3 membership accessing ps4 content

Yes you can access use one account on a PS3 and PS4

One membership for PS4, PS3 and PS Vita

while the link talks about Playstation Plus, all it is is an upgrade of a regular Playstation Network account which can be accessed in the same way. i can vouch for that from personal experience as i own all 3 consoles and i only have a normal PSN Account (No PS+)

On the PS3/4/Vita you can also view trophies collected on the other consoles and since you can't view this data in the offline mode on the PS3 or Vita and you need a PSN account to use the online mode then it stand to reason the account can be shared between the consoles.

Ofcause there is one catch, when your PSN account is on a console, that console is considered "activated" to your PSN account and there are limits, quick summery

• One (1) PS4™ as your 'Primary PS4' and one (1) other as a secondary PS4™
• Two (2) PS3™
• Two (2) portable PlayStation systems (PSP or PlayStation®Vita)

the link provided will also direct you to deactivating consoles. not sure what happens if you reach your limit and try and put your PSN account on another console since i don't own that many.

On a side note, you can have Multiple PSN accounts on one PS3/PS4, i have a AUS (Main), UK and US accounts on my PS3 and PS4, with the PS3 all content downloaded from any account will work on the system (have gotten UK and US DLC and played it on my profile with my AUs Account, works fine). with my PS4 i have yet to get into a situation where i needed DLC from the UK or US (and hopefully i never will)

As for content wise, it depends, some games when brought as PSN Voucher Codes to download a game for either system like Child of Light

Child of Light Deluxe Edition Includes:

• A Digital, Cross-Buy, Version of the game for PS3 or PS4
• An exclusive A2 Poster designed by Yoshitaka Amano.
• A 24 page art book with unrevealed Ark work.
• Two bonus digital content packs - Dark Aurora and Golem.
• An Igniculus key ring
• No disc in box
• Will Require UK/EU PSN account to download game

however most games/DLC can't. to my understanding the PS4 still lacks backwards compatibility so you can't play PSOne/2/3 games you brought on the PS3 on the PS4 and you can not play PS4 games on a PS3 (unless they are like Child of Light). i think the Playstation Store/Transaction History doesn't even list content that can't be used on the system

i would assume Movies and Music can be accessed between systems since i can't see any limitation posed by the hardware (as with the case with games) but i get movies/music the normal way, physical copies i actually own and can do whatever i want with (rip, burn, convert, backup, etc. as many times as i want)