Files

When adding items to your database, often you will upload one or more files (images, documents, etc.) associated with that item. An item can have as many files attached as you wish, or none.

Omeka Classic does not offer a way to upload files that are not attached to an item, except, depending on the theme, some branding files such as a header background or logo.

When uploading files from your computer, you can select multiple files in one location by highlighting them all, or use the "Add Another File" button to browse to files in separate locations.

File types

Omeka Classic accepts most common files and file types, and can be customized to accept or reject file types of your choice. You may wish to format your multimedia files according to what can best displayed and streamed in web browsers.

If you are seeing file-validation errors, please see more information about adjusting the accepted file types and extensions in the File Validation section of the Security Settings page.

File display order

If you have multiple files added to an item, you may click and drag the files into the preferred display order for both public and admin item pages.

The first file associated with an item will be used as its thumbnail in browsing and searching, as well as on timelines and in other features added by plugins.

File derivatives

Thumbnail images are automatically created for many file types (as of Omeka 2.0), including thumbnails from the first frame of videos.

Derivative images are generated as follows:

• A square thumbnail, used most commonly on browsing pages and in search results. This will clip the longer side of an image (centered) to the same length as the shorter side.
• An original-dimension thumbnail. You can choose to use square or original-dimension thumbnails throughout the public site, with a choice on the Settings tab of the Appearance page.
• A "full-size" image used on file view pages, by default 800 pixels on its longest side.
• The original-sized image as uploaded, available for download or viewing on file view pages.

You can control the size of each derivative file generated (square thumbnails and small original-dimension thumbnails, as well as full-size images) on the Settings tab of the Appearance page.

You can use the Derivative Images plugin to re-generate thumbnails for uploaded media if needed.

Items without attached files can display a default thumbnail rather than no thumbnail.

Thumbnail creation relies on the ability of your server's chosen thumbnail utility (the default being ImageMagick) and which file types it can process. If you have access to the config.ini file, you can manage thumbnail configuration.

Look up the utility you are using (such as ImageMagick, Imagick, or GD) to find out which file types it supports.

File size limitations

Omeka Classic imposes no file size limitations. Your server, however, may have restrictions on file upload sizes or speeds that may be causing problems. These limitations vary from server to server and we cannot change this for you. If you have a problem uploading files through the "Add New Files" interface, please first check with your hosting service or your local server administrator.

Batch-add files

To upload a large number of files, or large files, you may download and install the Dropbox plugin. It allows you to upload files from your computer directly into a folder in your installation, which you can then associate with existing items, or use to create new items. Note that this plugin is not associated with the "Dropbox" corporation and you do not need any external account to use this plugin.

File metadata

You may add a distinct set of Dublin Core metadata for each file uploaded. This will be stored and displayed separately from the associated item's metadata.

To add metadata, click the "Edit" button found to the right of the file name on admin/items/edit. You also may view or edit file metadata from the admin/items/show screen by clicking the file name under the heading "File Metadata."

Alt text

If a file does not have any metadata, as you can see in the above screenshot, Omeka uses the original filename (and path) as both title and alt text (see below). If the file has information in its Dublin Core Title property, that text will be displayed as the title for that file wherever it appears on the site.

Alternative text (alt) is displayed when an image cannot load. This information is also accessible to screen readers and other accessibility tools for the web. Best practices include using plain language to describe the content of the image without embellishment.

You may input alternative text for individual files by editing the file and drafting the text in the input area to the right of the file metadata. This will load wherever the file and its derivatives are displayed - in the administrative side, as thumbnails in browse and search screens, on the item view page, in exhibits, etc.

You can also configure a default file element to use for alt text for all image tags (that have a metadata value in that element). This is set in the Appearance Settings. This default will be overridden when text is supplied in the "Alt Text" field.

Multimedia files

As of version 2.4, Omeka Classic uses HTML5 audio and video tags when embedding audio and video. This means generally better support on newer browsers, but worse support on older ones and for older video formats especially.

By choosing from a few well-supported formats for audio and video files, you can provide a much better experience for your users across different platforms and devices.

Images

TIFF

TIFF files are not supported for display in most browsers. TIFFs can be ingested into Omeka Classic, where they will have derivative images generated in JPG format. The original TIFFs will be provided for download anywhere that Omeka calls the 'original' file. The JPGs will be displayed anywhere Omeka calls the 'fullsize', 'medium', or thumbnail images. This may depend on the theme.

Video

MP4

The MP4 container (.mp4 or .m4v) is the best-supported video format across browsers and platforms. By far the best choice for video that will work well across different browsers are .mp4 files with H.264 video and AAC audio.

.mp4 files can contain other types of video (or audio), including newer ones like H.265, and older ones like MPEG-4 Visual. Any video codec other than H.264 has much worse browser support.

Here is an example of an MP4 added to an item:

Other formats

The WebM (.webm) container with VP8 or VP9 video is supported by several browsers, but Internet Explorer and Safari are notable and significant exceptions.

The Ogg (.ogg, .ogv) container and Theora video are supported by some browsers, but there is little support among mobile browsers and no support at all on IE or Safari.

Audio

MP3

MP3 (.mp3) is one of the most common formats for compressed audio, and it enjoys wide support across browsers and from desktop to mobile. When an MP3 is added to an item, it will display as an embedded audio player with a play button, volume control, and a horizontal navigation.

Here is an example of an MP3 and a JPG both added to an item:

AAC

AAC is a somewhat newer format than MP3, but it also is well supported in most browsers. The widest support is for AAC in an MP4 container (this usually carries the file extension .m4a), with somewhat lesser support for other containers and formats (often found with a .aac extension).

Other formats

WAV or WAVE (.wav) audio is supported by most browsers (with the notable exception of Internet Explorer). The major downside for use on the Web is that WAV audio is uncompressed, so it takes up vastly more storage space and bandwidth than the compressed formats listed above. If feasible, it’s best to use one of those instead of WAV.

Ogg Vorbis audio (.ogg, .oga) is a compressed format like MP3 and AAC, but it has much less widespread support. Expect Vorbis audio to only work on Firefox, Chrome, and Android.

Opus (.opus) is one of the newer available audio formats. For the time being, it has a similar problem as Vorbis: a lack of support among browsers, but there are signs that Opus could gain more support in the future.

Legacy formats

There are a lot of media files that aren’t in any of the formats listed here. With certain add-ons or on certain platforms (like Safari on Mac, in many cases), it can be possible to embed some of those files with HTML5, but expect many or most users to be unable to play them. Browser plugins can also play many file types, but browsers are steadily reducing and removing their support for these kinds of plugins.

For old media, often the best choice is to just present a download link so the viewer can play or convert the file locally. This is what Omeka does when it doesn’t recognize a file type or when a browser reports that it can’t play a file.

File formats which result in a download link, rather than an embedded playback, include:

• Video: .avi, .wmv
• Audio: .aiff (except Safari), .midi, .wha
• Image: .tiff (we generate JPG derivatives for display, but offer the original TIFF for download.)

If you do not see a format listed here that you think should be, try it out and let us know the results.