Replay is a feature in Super Smash Bros. Brawl that allows players to review previous gameplay moments. Once a match ends, players can press the Z button on the results screen to save the replay on to the SD Card or the Wii itself. Replays can only be save if the match lasted less than 3 minutes, Sudden Death included. Hacks, such as Balanced Brawl, can remove this limit.
When saved, replays will be named
 Smash Service
Prior to June 30, 2009, players could send their replays to be used for the Smash Service; after June 30, no more replays, custom stages, or screenshots would be accepted. One month later, on August 1, replay data was no longer being sent. Replays used for Smash Service were all from Stadium mode, especially Home-Run Contest and Target Smash!!, due to their typically shorter length and file size.
Contrary to what may be expected, a replay is not saved as a video recording of the match. Instead, the input data from the match, the match's random number seed and the general rules are saved, so when a replay is watched, the game in fact re-generates the match from the data. This makes replays much smaller in file size than a video file, and it also allows pausing and camera movement during the replay.
Replays do not save the players' names, but this can be changed with a cheat code. For online battles, the game saves each player's server number and client number. When a player battles online, the player is seen as player 1 on his screen (client), but that may not be true for the server. In saved replays, each player's color and the numbers above the characters' heads indicate the client numbers (the ones that were seen on the screen of the one who saved the replay), whereas the order in which the character portraits appear on the bottom indicate the server numbers.
While playing online in the "With Anyone" mode, the characters' scores will not appear on the screen above the characters' icons. However, when battles are saved as replays, the replays will show the score numbers above the characters' icons as if the players were playing a Group Brawl with "Score Display" turned on in the brawl settings.
If a character or other element is loaded during a match faster than expected (such as because of pausing or online lag), then the replay of that match will to "freeze" and finish loading the element before it can continue.
A common error noted in replays is that they may "desync" over time; the effects vary, though among the most common are actions occurring that did not previously occur, excessive lag followed by significantly increased playback speed, and the replay abruptly ending. With the Pokémon Trainer, particularly unusual effects can occur, such as him sending out a Pokémon which never loads or leaves the revival platform . Replays of Wi-Fi matches are more likely to desync than local matches due to the frequent lag experienced in games, but local replays can also be subject to the problem. The cause of "desyncs" is unknown, though it is speculated it has to do with save data of replays becoming corrupted by some outside factor. In addition, it's possible for a replay that plays fine to randomly desynchronize when played again, and after some tries, play correctly again.
A very rare bug causes saved replays to have idiosyncratic values in its timestamp, such as 781/88/2008 280:-480.
 Synchronization glitches