Derivative Media Optimizer

By Daniel Berthereau Create and cache derivative files for items (zip, pdf, iiif, etc.) and optimize audio and video files for performance and cross-browser compatibility.
Download 3.4.11

Derivative Media Optimizer (module for Omeka S)

New versions of this module and support for Omeka S version 3.0 and above are available on GitLab, which seems to respect users and privacy better than the previous repository.

Derivative Media is a module for Omeka S that optimizes files for the web: it creates derivative files from audio and video files adapted for mobile or desktop, streamable, sized for slow or big connection, and cross-browser compatible, including Safari. Multiple derivative files can be created for each file. It works the same way Omeka does for images (large, medium and square thumbnails).

At item level, some more formats are supported: - alto: Xml format for OCR. When alto is available by page, a single xml may be created. It is useful for the module Iiif Search, because the search can be done quicker on a single file. - iiif/2 and iiif/3: Allow to cache IIIF manifests (v2 and v3) for items with many medias or many visitors, so it can be used by module Iiif Server or any other external Iiif viewer. - text: If text files are attached to the item, they can be gathered in a single one. - text: If text is available in media values "extracttext:extracted_text", they can be gathered in a single one. - pdf: concatenate all images in a single pdf file (require ImageMagick). - pdf2xml: extract text layer from pdf and create an xml for iiif search. - zip: zip all files. - zip media: zip all media files (audio, video, images). - zip other: zip all other files.

The conversion uses ffmpeg and ghostscript, two command-line tools that are generally installed by default on most servers. The commands are customizable.

The process on pdf allows to make them streamable and linearized (can be rendered before full loading), generally smaller for the same quality.


Some formats used by this module requires server packages: - ffmpeg for audio and video - ghostscript with command gs for pdf - pdftotext from package poppler-utils for format pdf2xml

If you use them, they should be installed on the server and available in the path.

First, install the required module Common.

You can use the release zip to install it, or use and init the source.

  • From the zip

Download the last release [] from the list of releases and uncompress it in the modules directory.

  • From the source and for development:

If the module was installed from the source, rename the name of the folder of the module to DerivativeMedia.

See general end user documentation for Installing a module and follow the config instructions.


Configuration of commands

Set settings in the main settings page. Each row in the text area is one format. The filepath is the left part of the row (mp4/{filename}.mp4) and the command is the right part.

The default params allows to create five derivative files, two for audio, two for video, and one for pdf. They are designed to keep the same quality than the original file, and to maximize compatibility with old browsers and Apple Safari. The webm one is commented (a "#" is prepended), because it is slow.

You can modify params as you want and remove or add new ones. They are adapted for a recent Linux distribution with a recent version of ffmpeg. You may need to change names of arguments and codecs on older versions.

For pdf, the html5 standard doesn't give the possibility to display multiple sources for one link, so it's useless to multiply them.

Ideally, the params should mix compatibilities parameters for old browsers and Apple Safari, improved parameters for modern browsers (vp9/webm), and different qualities for low speed networks (128kB), and high speed networks (fiber).

Then, in the site item pages or in the admin media pages, all files will be appended together in the html5 <audio> and <video> elements, so the browser will choose the best one. For pdf, the derivative file will be used automatically by modules [Universal Viewer] (via IIIF Server) and [Pdf Viewer].

Bulk creation

You can convert existing files via the config form. This job is available in the module Bulk Check too.

Note that the creation of derivative files is a slow and cpu-intensive process: until two or three hours for a one hour video. You can use arguments -preset veryslow or -preset ultrafast (mp4) or -deadline best or -deadline realtime (webm) to speed or slow process, but faster means a lower ratio quality/size. See ffmpeg wiki for more info about arguments for mp4, ffmpeg wiki too for webm, and the browser support table.

For mp4, important options (preset and tune) are explained here. For webm, important options (preset and tune) are explained here.

In all cases, it is better to have original files that follow common standards. Check if a simple fix like this one is enough before uploading files.

The default queries are (without ffmpeg or gs prepended, and output, appended):

# Audio
mp3/{filename}.mp3   = -c copy -c:a libmp3lame -qscale:a 2
ogg/{filename}.ogg   = -c copy -vn -c:a libopus
aac/{filename}.m4a   = -c copy -c:a aac -q:a 2 -movflags +faststart

# Video. To avoid issue with Apple Safari, you may add mov before mp4.
webm/{filename}.webm = -c copy -c:v libvpx-vp9 -crf 30 -b:v 0 -deadline realtime -pix_fmt yuv420p -c:a libopus
mov/{filename}.mov   = -c copy -c:v libx264 -movflags +faststart -filter:v crop='floor(in_w/2)*2:floor(in_h/2)*2' -crf 22 -level 3 -preset ultrafast -tune film -pix_fmt yuv420p -c:a aac -qscale:a 2 -f mov
mp4/{filename}.mp4   = -c copy -c:v libx264 -movflags +faststart -filter:v crop='floor(in_w/2)*2:floor(in_h/2)*2' -crf 22 -level 3 -preset ultrafast -tune film -pix_fmt yuv420p -c:a libmp3lame -qscale:a 2

# Pdf (supported via gs)
# The default setting "/screen" output the smallest pdf readable on a screen.
pdfs/{filename}.pdf' => '-dCompatibilityLevel=1.7 -dPDFSETTINGS=/screen
# The default setting "/ebook" output a medium size pdf readable on any device.
pdfe/{filename}.pdf' => '-dCompatibilityLevel=1.7 -dPDFSETTINGS=/ebook
# Here an example with the most frequent params (see
pdfo/{filename}.pdf  = -sDEVICE=pdfwrite -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -dCompatibilityLevel=1.7 -dSubsetFonts=true -dCompressFonts=true -dEmbedAllFonts=true -sProcessColorModel=DeviceRGB -sColorConversionStrategy=RGB -sColorConversionStrategyForImages=RGB -dConvertCMYKImagesToRGB=true -dDetectDuplicateImages=true -dColorImageDownsampleType=/Bicubic -dColorImageResolution=300 -dGrayImageDownsampleType=/Bicubic -dGrayImageResolution=300 -dMonoImageDownsampleType=/Bicubic -dMonoImageResolution=300 -dDownsampleColorImages=true -dDoThumbnails=true -dCreateJobTicket=false -dPreserveEPSInfo=false -dPreserveOPIComments=false -dPreserveOverprintSettings=false -dUCRandBGInfo=/Remove

It's important to check the version of ffmpeg and gs that is installed on the server, because the options may be different or may have been changed.

External preparation

Because conversion is cpu-intensive, they can be created on another computer, then copied in the right place.

Here is an example of a one-line command to prepare all wav into mp3 of a directory:

cd /my/source/dir; for filename in *.wav; do name=`echo "$filename" | cut -d'.' -f1`; basepath=${filename%.*}; basename=${basepath##*/}; echo "$basename.wav => $basename.mp3"; ffmpeg -i "$filename" -c copy -c:a libmp3lame -qscale:a 2 "${basename}.mp3"; done

Another example when original files are in subdirectories (module Archive Repertory):

# Go to the root directory (important to recreate structure with command below).
cd '/var/www/html/files/original'

# Convert all files.
find '/var/www/html/files/original' -type f -name '*.wav' -exec ffmpeg -i "{}" -c copy -c:a libmp3lame -qscale:a 2 "{}".mp3 \;

# Recreate structure of a directory (here the destination is "/var/www/html/files").
find * -type d -exec mkdir -p "/var/www/html/files/mp3/{}" \;

# Move a specific type of files into a directory.
find . -type f -name "*.mp3" -exec mv "{}" "/var/www/html/files/mp3/{}" \;

# Remove empty directories.
rmdir "/var/www/html/files/mp3/*"

# Rename new files.
find '/var/www/html/files/mp3' -type f -name '*.wav.mp3' -exec rename 's/.wav.mp3/.mp3/' "{}" \;

IMPORTANT: After copy, Omeka should know that new derivative files exist, because it doesn't check directories and formats each time a media is rendered. To record the metadata, go to the config form and click "Store metadata".

Fast start

For mp4 and mov, it's important to set the option -movflags +faststart to allow the video to start before the full loading. To check if a file has the option:

ffmpeg -i 'my_video.mp4' -v trace 2>&1 | grep -m 1 -o -e "type:'mdat'" -e "type:'moov'"

If output is mdat and not moov, the file is not ready for fast start. To fix it, simply copy the file with the option:

ffmpeg -i 'my_video.mp4' -c copy -movflags +faststart 'my_video.faststart.mp4'

See ffmpeg help for more information.

Protection of files

To protect files created dynamically (alto, text, zip…), add a rule in the file .htaccess at the root of Omeka to redirect files/alto, files/zip, etc. to /derivative/{type}/#id.

Theme with resource block and view helper

Use the resource block "Derivative Media List" to display the list of available derivative of a resource.

Or use the view helper derivatives():

<?= $this->derivatives($resource) ?>


  • [ ] Adapt for any store, not only local one.
  • [ ] Adapt for thumbnails.
  • [ ] Adapt for models.
  • [ ] Improve security of the command or limit access to super admin only (in main settings anyway).
  • [ ] Add a check for the duration: a shorter result than original means that an issue occurred.
  • [ ] Add a check for missing conversions (a table with a column by conversion).
  • [ ] Add a check for fast start (mov,mp4,m4a,3gp,3g2,mj2).
  • [ ] Finalize for pdf.
  • [ ] Add a check of number of job before running job CreateDerivatives.
  • [ ] Pdf to tsv for iiif search


Use it at your own risk.

It’s always recommended to backup your files and your databases and to check your archives regularly so you can roll back if needed.


See online issues on the module issues page.


This module is published under the CeCILL v2.1 license, compatible with GNU/GPL and approved by FSF and OSI.

This software is governed by the CeCILL license under French law and abiding by the rules of distribution of free software. You can use, modify and/ or redistribute the software under the terms of the CeCILL license as circulated by CEA, CNRS and INRIA at the following URL "".

As a counterpart to the access to the source code and rights to copy, modify and redistribute granted by the license, users are provided only with a limited warranty and the software’s author, the holder of the economic rights, and the successive licensors have only limited liability.

In this respect, the user’s attention is drawn to the risks associated with loading, using, modifying and/or developing or reproducing the software by the user in light of its specific status of free software, that may mean that it is complicated to manipulate, and that also therefore means that it is reserved for developers and experienced professionals having in-depth computer knowledge. Users are therefore encouraged to load and test the software’s suitability as regards their requirements in conditions enabling the security of their systems and/or data to be ensured and, more generally, to use and operate it in the same conditions as regards security.

The fact that you are presently reading this means that you have had knowledge of the CeCILL license and that you accept its terms.


  • Copyright Daniel Berthereau, 2020-2024

First version of this module was done for Archives sonores de poésie of Sorbonne Université.

Version Released Minimum Omeka version
3.4.11February 26, 2024 [info]^4.0.0
3.4.10February 19, 2024 [info]^4.0.0
3.4.9November 27, 2023 [info]^4.0.0
3.4.8October 30, 2023 [info]^3.1.0 || ^4.0.0
3.4.7September 04, 2023 [info]^3.1.0 || ^4.0.0
3.4.6May 22, 2023 [info]^3.1.0 || ^4.0.0
3.4.5May 15, 2023 [info]^3.1.0 || ^4.0.0
3.4.4May 01, 2023 [info]^3.1.0 || ^4.0.0
3.4.3March 13, 2023 [info]^3.1.0 || ^4.0.0 12, 2022 [info]^3.1.0