Usage

The mediaGalleries API lets you prompt the user for permission to access media galleries on the user's computer. The permission dialog contains common media locations for the platform and allows the user to specify additional locations. From those locations, only media files will be present in the file system objects.

Manifest

The media galleries API has two axes of permission parameters:

the locations that can be accessed
the type of access

These two axes and the permission parameters on each axis are described in the table below:

Axis	Parameter	Effect
Locations	none	If you do not specify a location permission parameter, your app will not be able to access any media galleries until the user grants permission to access specific media galleries at runtime using the media gallery permission dialog.
Locations	"allAutoDetected"	Grants your app access to all auto-detected media galleries on the user's computer. This permission causes an install-time prompt to be displayed indicating that the app will have access to the user's media files.
Access type	"read"	Grants your app the right to read files in media galleries.
Access type	"copyTo"	Grants your app the right to copy files into media galleries. Only valid media files that Chrome is capable of playing or displaying are permitted; files that Chrome is not able to validate will result in a security error.

Notes:

The media gallery permission dialog can be triggered programmatically. The user may have alternate media locations, so even if you specify "allAutoDetected" permsission, it is still important to provide a mechanism to open the permission dialog in your app.
There is no write access to media galleries due to the file validation requirement. However, you can write files to a different file system like the temporary file system, and then copy the files into the desired media gallery.
You can specify "read" and "copyTo" to obtain both types of permissions to media galleries.
Access type permissions do not trigger an install-time prompt by themselves. However, the type of access will be reflected in the media gallery permission dialog, as well as the install-time prompt if "allAutoDetected" permission is requested.

Below is an example of a manifest file with mediaGalleries permissions:

{
  "name": "My app",
  ...
  "permissions": [
    { "mediaGalleries": ["read", "allAutoDetected"] }
  ],
  ...
}

This example manifest file will trigger an install-time permission prompt, and let the app read from all auto-detected media galleries on the user's computer. The user may add or remove galleries using the media gallery permission dialog, after which the app will be able to read all the media files from galleries that the user selected.