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Movie files are highly sensitive to timing, so some little difference may cause the movie to play back incorrectly. For example, the character might suddenly stop moving, or wander aimlessly, or die. Mario might run continuously into the side of a pipe. Mega Man X might jump into a pit. Or the game might not even leave the starting menu.
Do note that some TASes may have potentially confusing actions that may be mistaken for desyncs.

Movie Watching

When the movie you’re trying to view desyncs, there are a few possible causes.

You don’t have the right ROM.

There are generally three versions of games: Japan, Europe and USA version, sometimes marked at the end of the ROM name by (J), (E), or (U) respectively. If you have the wrong one, the movie will likely go out of sync sooner or later.
Sometimes games have multiple revisions, (e.g. REV1, REV2), multiple fixes or hacks. If you have the wrong one, your movie will probably go out of sync.
The author may provide the name of the ROM. It is recommended (but not required) to rename ROMs using GoodTools in order to standardize ROM names.
Do not ask us (the author of this site or the people at the TASvideos forum) to send you ROMs or BIOS images. Any such messages will be deleted.
It is generally best to check the hash of the ROM for an exact match. Hashes ensure, in practice, that you have exactly the same file as the author. Exact hash values using common algorithms such as MD5 and SHA1 are often posted in the discussion threads.

You don’t have the right version of the emulator.

Ensure you used the correct emulator version. Usually, the author will state the version. If not stated, assume it is the most recent version.

Your emulator settings differ too much.

If you feel you may need to change the settings, the solution is usually found in the author’s description of the movie.

You have external codes on (ex. Game Genie codes)

Turn them off.

Replay is not quite deterministic

There's not much you can do about this except try and hope. Sometimes runs desync when played back one way and don’t desync when played back another way.

Movie Making

It happens quite often, especially on newer emulators. You carefully construct your TAS and when you check your progress, the movie goes off at some point and does something wrong.
Most desyncs are a result of inconsistent savestates, when an emulator or savestate error causes you to start using a wrong savestate. Once that happens, your movie starts to go down the wrong track. If you notice this happening, recreate your savestates at the most recent point where the movie plays as intended.
While you are making a movie, make it a habit to periodically play through your whole movie to verify that it syncs, and always make a backup of the working copy.
If your run desyncs, no one can help you recover the lost work. It is up to you to be careful.
There are a number of causes of inconsistent savestates:

Emulator problems

PCSX, Mupen64, and FBA-rr



Visual Boy Advance


Savestate problems

Other problems

You have external codes on (ex. Game Genie codes)

Be very careful that you don't have external codes on. It is easy to miss. If your movie requires external codes to play back correctly, TASVideos cannot accept your movie.

You changed the settings by accident

If this happens, try to rectify what you can. Do not continue with inconsistent settings.

Replay is not quite deterministic

If you discover that different ways of playing the movie yield different results, it could mean an emulation issue with that game, and it is recommended you stop TASing it until the problem is diagnosed and fixed.

Game suddenly resets

Some versions of some emulators may have a bug that inserts spurious resets in some conditions, resulting in a movie that suddenly resets the game. This can be fixed by editing the movie file to remove the spurious reset.

DesyncHelp last edited by Samsara on 8/7/2023 9:03 PM
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