The big change is basically that we now typically specify exactly which integer approximation to the (real-valued, “ideal”) DCT to use; this means the decoder and encoder is much likely to fall out of sync. As a bonus, this means we can use a slightly worse but much faster approximation without catastrophes happening, and possibly also make it exactly invertible.

https://fgiesen.wordpress.com/2013/11/04/bink-2-2-integer-dc... has a ton of technical information if you want to dive into it.