In short, they are both more or less correct and mean approximately the same thing.
In long, there are differences but the differences will only be perceived if specifically contrasted or emphasized. I will contrast three statements.
- The video was great. I wish it was longer.
- The video was great. I wish it had been longer.
- The video was great. I wish it were longer.
In number 1, the wish is about the present. It sounds like you are still in a state of wishing and if you could have your way, the movie would be be longer in the future (regardless of how ridiculous that is).
Number 2 is about the past. It sounds like you are specifically talking about an instance of watching the movie and you wish that in that one instance, the movie had been longer.
Number 3 uses a dying part of English grammar called the subjunctive mood (in the present). It is used to express wishes that do not have a reasonable chance of coming true. As I've said, it is not knowingly used by English speakers but is still heard sometimes. The past subjunctive is "had been" so it winds up being the same as number 2.
Number 2 and 3 are definitely correct. Number 1 could be thought of as incorrect but no one would be certain and everyone would understand.