The idea of using video replays in soccer to help referees make decisions is something that had long been discussed and never acted upon. But that is quickly changing and, now, it's finally on the verge of becoming reality.

On Monday, FIFA took an early but real step toward adding video replay by meeting with technology companies that will help make FIFA-sanctioned trial runs possible. Among the questions FIFA will have to sort out: How can they standardize video replay procedures and equipment globally, so video replay in Major League Soccer affects the game just as it would in, say, the Bundesliga?

After all, there will still be a significant human element: Video assistant referees, or VARS as they will be known, must interpret video replays and communicate their findings to the referees on the field. It would not be an automatic decision, like goal-line technology provides.

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But we have a pretty good idea of how it will work because MLS has quietly been running its own trials on video replay for the past three seasons. The trials, which were done by Real Salt Lake, the Vancouver Whitecaps and the Philadelphia Union, were conducted behind the scenes by stopping just short of actually communicating with refs and affecting the calls in the game.

It was those trials, along with ones by the Dutch Football Association, that convinced FIFA to change its laws to allow the possibility of video replay. Earlier this month, MLS was selected as one of the competitions to conduct a round of official trials for FIFA along with four others: Australia's A-League, Germany's Bundesliga, Portugal's Liga NOS, and several competitions operated by the Brazilian Football Confederation.

So how did MLS do their experiments, and what could video replay ultimately look like?

What plays will be reviewed?

Video replay trials have centered around three types of plays: red cards, penalty kicks and goals.

There are certainly other types of plays refs can get wrong and fans would like to see reviewed, but video review will generally be limited to only those three game-changing plays. That means if a player should've earned a red card and only earned a yellow card, for example, the play would not be subject to video review.

What remains to be seen is how that could affect the behavior of referees. If a referee knows that a red card will trigger a review, he or she may be more likely to give a red card and ensure it's the right call, rather than err on a less harsh call. That could mean more red cards than ever before.

Only red cards, goals and penalty kicks will trigger a review, but FIFA has added an ongoing responsibility of looking for cases of mistaken identity -- if a ref cards the wrong player, video referees can intervene.

Would video replay disrupt the flow of the game?

It shouldn't. The goal of MLS' trials has been to maintain the flow of the game and only use natural stoppages, which they say they've achieved.

According to the findings from the MLS trials, there is a natural stoppage of time that lasts about one minute after the three types of game-changing plays that they have been reviewing in tests.

Think about it like this: While you're on your couch watching replays on TV because the game has stopped due to players arguing with the ref, players celebrating or whatever else, a referee would be in a booth somewhere watching replays too.

MLS has found that off-site referees can review video of a play and reach a determination within about 20 seconds, leaving plenty of time to communicate to the referee before the game restarts.

Of course, there's again the question of whether video replay could change a referee's behavior. Will refs stall or pause the proceedings as they await word from the video officials? That will remain to be seen, but in normal circumstances, early indications are that such stalling wouldn't be necessary due to the natural stoppages of the game.

How would video replay change calls?

The last time major technology was introduced to soccer was via goal-line technology, which made its debut at the World Cup in 2014 -- and it's about as straight-forward as technology can get. Did the ball cross the line completely, and thus was a goal scored: yes or no?

But video replay retains a very human element. If you've ever sat next to a friend watching a slow motion replay during a match, you probably know what it's like: One of you swears the play you're watching deserved a red card, while the other one says they don't see anything on the replay to indicate such a harsh punishment.

In MLS trials, video referees did not make or recommend specific calls, but communicated information about what the replays showed: The studs were showing, the foul was committed outside the box, the player's hand was tucked inside the body, and so on. Based on that information, the ref on the field can make a call.

But FIFA is experimenting with a step beyond that -- if a ref isn't willing to accept the information from the video referee, he or she can walk to the sideline and view the replay on a monitor.

Will referees always get calls correct with video replay?

There's something about incorrect calls that makes soccer the special game that it is. Perhaps it's the injustice of incorrect calls firing up a fanbase or the debate that rages on after a controversial call, but for better or worse, incorrect calls keep the game interesting.

So could soccer risk losing something special by adding video replay?

As Todd Durbin, MLS' head of competition and player relations, put it back in May: "When you start bringing replay in, it does help you in certain instances, but it also does bring about other ambiguities."

Going back to the scenario where you're with a friend sitting on the couch, arguing about what the correct call should be based on a video replay, it seems doubtful that video replay will guarantee correct calls all the time. The video referees are human, too.

While replay would probably eliminate the most egregiously wrong calls, the fact also remains is that many of the rules in soccer are subjective. As long as referees are tasked with the impossible job to determine a player's intent, there will be controversial calls.

When will video replay be used in real games?

The trials are starting in the same stage as MLS' have been conducted: behind the scenes without actually affecting the outcome of the officiating. FIFA will review the results from that phase early next year.

Assuming all goes well, the second phase of experimentation will begin in 2017, which will consist of actually using video replay refs in competition.

FIFA says they hope to have gathered enough information from the trials to make a decision on approving it for official matches by 2018 at the earlier or 2019 at the latest.