Saving replay

Can anyone tell me what the requirements are to be able to save a replay ? Can’t seem to find anything on it .

Depends what you mean by saving a replay?

By default any match you play online or watch online is saved into your Battle Log and from there you can watch the last 50 or so saved matches and then choose to save them to your replay list which can then be uploaded onto your replay channel. In addition to that if you win a certain number of ranked games in a row online you can choose to upload the last game to the replay channel.