Output of the Build

The earlier “AssetBundle workflow” section describes how to build AssetBundles using BuildPipeline.BuildAssetBundles. That API call writes the results of the build process into the specified output directory, including the AssetBundle files and a .manifest file for each AssetBundle. This section describes the details of the files written by the build process.

The AssetBundle File

This is the file that lacks the .manifest extension and what you’ll be loading in at runtime in order to load your Assets.

The AssetBundle file is an archive that contains multiple files internally. This is an example structure for a normal AssetBundle:

The main file uses Unity’s binary SerializedFile format. It contains the AssetBundle object and the objects from all the Assets that are included (explicitly or implicitly) in the AssetBundle. Any audio, video content would be stored in a .resource file, and any texture data would be stored in a .resS file.

The content inside a SceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary AssetBundle is similar, but it is optimized for stream loading of individual Scenes. It will contain two SerializedFiles per scene.

The Manifest File

For every AssetBundle generated, including the additional Manifest Bundle, an associated manifest file is generated. The manifest file has the extension .manifest and can be opened with any text editor. It contains information such as the cyclic redundancy check (CRC) data and dependency data for the bundle. The manifest files for normal AssetBundles will look something like this:

ManifestFileVersion: 0
CRC: 2422268106
Hashes:
  AssetFileHash:
    serializedVersion: 2
    Hash: 8b6db55a2344f068cf8a9be0a662ba15
  TypeTreeHash:
    serializedVersion: 2
    Hash: 37ad974993dbaa77485dd2a0c38f347a
HashAppended: 0
ClassTypes:
- Class: 91
  Script: {instanceID: 0}
Assets:
  Asset_0: Assets/Mecanim/StateMachine.controller
Dependencies: {}

Which shows the contained assets, dependencies, and other information.

The Manifest Bundle

There are two additional files generated by the build.

The first is a small AssetBundle that is named after the directory that it’s located in (where the AssetBundles were built to). This file is called the Manifest Bundle and it contains the AssetBundleManifest object which will be useful for figuring out which bundle dependencies to load at runtime. To learn more about how to use this bundle and the manifest object, see documentation on Using AssetBundles Natively.

A .manifest file is also generated for the Manifest Bundle. Its content will look something like this:

ManifestFileVersion: 0
AssetBundleManifest:
  AssetBundleInfos:
    Info_0:
      Name: scene1assetbundle
      Dependencies: {}

The .manifest file for the Manifest Bundle records how AssetBundles relate, and what their dependencies are. This is similar to the information recorded by the AssetBundleManifest object, inside the Manifest Bundle, and because it is a text file it is convenient for human readability and parsing by external tools. This .manifest file is important for preventing code stripping for types that you use in your AssetBundle, if those types are not used by the content in your Player Build. If code stripping is enabled in your Player SettingsSettings that let you set various player-specific options for the final game built by Unity. More info
See in Glossary then you should pass the path to this manifest when performing Player Builds, by setting BuildPlayerOptions.assetBundleManifestPath. For more information about code stripping see Distribution size and code stripping.

Note: When building using the Addressables package instead of BuildPipeline.BuildAssetBundles the same format of AssetBundle file is written, but there are no manifest files, and no Manifest Bundle is generated. Refer to the Addressables documentation for more details.