one iap for multiple device and OS

An app can play stuff that they download using a subscription purchased outside the app. That is how 'netflix' et al can operate under the guidelines. If your app is purchasing something that allows it to do more than download and play content then you must purchase it through Apple IAP.

I have question about iap Guideline from Apple.

Forums are typically dev/dev, so...opinions and anecdotes are more likely. Apple engrs. respond when they have time and will have an  logo next to their forum user name. Call Apple up if you want to talk to dev support. Numbers here.

I have an application on the web, users can purchase a subscription (with auto renew). I'd like to develop an app for iOS and create the same system.

You can do that, but it won't be via IAP. You can't have both work together as 'same system'.

I know that I can create an iap subscription (and I'll do it) but I don't want that my web users have to pay a second sub in ipad. And my iPad user buy a second sub in my website.

No. If IAP/Apple is involved in payment system, you're not allowed to hybridize an external ad-hoc system. See above.

I'd like one purchase for multiple device and OS. If a users buy a subscription on his ipad, this sub is also activate on website, android... Is it authorized by apple ?

See above.

I know that netflix, spotify and other app like that work with one purchase but is it a commun things or is it authorized because they are big company and they negotiate with apple ?

If the question is are you/we like big providers, no, of course not. BTW...don't confuse in-app subscription w/ 'in app purchase'.

Thanks for answer.

I'll contact Apple to discuss about iap and limitations of guideline.

Thanks for advices and informations.