discipline

hi

does anyone know how to discipline a asd child? my 4 year old son is very hyperactive and quick to aggression. so as you can imagine he is very easily upset and quick to have a meltdown. i am trying to catch it before he has a meltdown but it can be so quick it can be impossible to stop. i know his triggers but can not always eliminate them for example like his little sister crying. i generally use timeout for any hitting but when he gets worked up i know he finds it hard to not hit. also if i did put him on timeout when having a meltdown it would just esculate the problem. at the moment when he has a meltdown i first do what i can to calm him down and feel better. but when he is then calm what do i do to then get him to realise that he can't hurt people? he is also so heavyhanded when playing and doesn't realise he is hurting other children. i don't know what to do. i don't want him to hurt people and lose friends as he is already saying to me he's noticed he's different to other people, losing friends would make it harder for him.