Reducing the size of media files (image, audio and video)


There are several reasons for wanting to reduce the size of files uploaded to Blackboard.

  1. To reduce the overall size of the Blackboard database
    An unnecessarily large database

    • costs the University money (in increased Blackboard licence fees)
    • can adversely affect system performance.
  2. To benefit your students
    Larger files take longer to download – causing problems especially for students accessing Blackboard through a slow wifi connection and/or on a mobile device.

This guide will suggest ways of reducing the size of various file types.

Word documents

Word documents containing a large number of images may swell to an unnecessarily large size. In versions of a document which are primarily going to be viewed online, it is worth compressing the images to reduce overall filsesize – see Reduce the file size of a picture in Microsoft Office (covers Office generally, including MS Word).


PowerPoint presentations

Over-large filesizes are normally caused by

  • lots of high quality images
  • embedded audio or video files

To reduce the filesize of presentations which will primarily be viewed online, see these guides


Reduce the file size of a picture in Microsoft Office (covers MS Office generally, including PowerPoint)

Audio and video media

You can Compress your media files to reduce the file size.

But the best option is probably to Optimise Media Compatibility – this will reduce the size of large audio or video files embedded into the presentation, but also ensure that the media files are saved in a format which will work across devices and operating systems.

Adobe Acrobat documents

Most PDF files will have been generated from other programmes such as MS Word or Powerpoint. If creating a PDF which is primarily going to be viewed online, it is worth compressing the images to reduce overall filesize. Assuming you only have access to the free Acrobat Reader, you will need to do this in the originating software (e.g. Word) – before saving as a PDF.

This Microsoft page provides guidance on saving to PDF from various Office programmes: Save or convert to PDF from MS Office.

There are equivalent help pages for users of

These include options for compressing images when saving to PDF.


As stated above, high quality images in Word, PowerPoint or PDF files can significantly increase file size.

If you are simply uploading a picture to your Blackboard course, this should also be reduced to an appropriate size – both in terms of filesize and dimensions in pixels. Photographs taken on a camera, or even on a phone, will probably be much larger than needed for display on your Blackboard course.

It is best to save the image at an appropriate pixel size before uploading it to Blackboard – rather than just reducing the size at which it displays inside Blackboard. There will be exceptions, of course, but it is probably rare that an image displayed within Blackboard needs to be larger than 800 x 600 pixels.

You can resize files using Gimp (available via Apps Anywhere) or using a range of free online tools. For Windows 10 users, the simplest option is to use the built-in Microsoft Photos app:

MS Photos - resize image

Audio files

  • Audio files should always be saved in MP3 format.
  • You can use VLC Player (available via Apps Anywhere) to convert files e.g. from WAV to MP3.
    For help see the VLE help site: Convert Audio Formats using VLC Media Player.
  • Keep your audio files short – if necessary split a longer recording into several 10-15 minute chunks.

Video files