ed app microlearning mobile lms

Optimal File Sizes

Key Takeaway: Minimise the size of your lessons by streaming your videos, and using images optimised for mobile.

For most users, lesson download size is not a concern. Lessons are optimised by default, and learners can download entire courses in seconds. However, for those instructional designers who want to use lots of imagery in their lessons, plan to upload videos for knowledge transfer, or are looking to cover off cases where learners can only access their lessons on low quality internet connections, this article can help you reduce download times, and make your lessons micro in more than just length.


Videos should be set to play on demand where possible. This means that they are not packaged in the download of the lesson, but streamed while the learner is viewing the video, giving them the quickest possible access to their lessons.

play on demand

While this means that using smaller videos will not impact lesson size (as long as those videos are set to play on demand), using smaller videos provides a better viewing experience for users who have poor internet connections, when they view those videos in-lesson.

As a general rule, we have found that videos at 480p (approximately 858x480px) are more than enough for mobile viewing. If you are concerned about the impact on video quality at lower resolutions, this can be increased (with the understanding that there may be a tradeoff against ensuring a smooth viewing experience, for users on poorer connections). Read more about using videos on Ed here.


Images used in Ed lessons do not need to be overly large. Remember that some of your learners may be accessing the content over potentially slow mobile data connections.

As a rule, images on interactive templates (such as Image Multiple Choice or Drag to Match should be no larger than 600x600px, and those used in content templates should only reach 800x800px (unless you are using a template which requires a high resolution image, such as Image Waypoints). It is possible to use images which are smaller or larger than these suggested sizes, however this may negatively impact the quality of the image display in the lesson, and the download size of your lesson.

Where possible, images should also be in the jpg file format, as jpg images have built in file compression, which provides images of a far smaller size than those saved as pngs. This rule also applies to background images you use in your lesson branding.

For those of you looking to provide the smallest possible lesson downloads, an image size optimisation program could also be of use. At Ed, all of our content authors run any images they plan to use in a lesson through ImageOptim, a free program which reduces their file size without impacting their visual quality. While this does not typically greatly reduce the size of jpg images (as these are already optimised by default), it is possible to change from the default settings to allow greater file compression, with the understanding that this would come with a slight sacrifice to image quality.

How to identify lesson size problems

It is possible to see the total file size of your lesson while editing it (viewable in the top right of the authoring tool). If you see this value going over 5mb, there might be an oversized image in the lesson, or a video which is not set to stream. This lesson size value updates on refreshing the page (so don’t be worried if you press save and don’t immediately see a change in size).

file size location

When you find a lesson which is a lot bigger than other lessons, you can use the scorm-out LMS feature to help identify the problem. This provides you with a zip file of the entire lesson, and puts all the images in one helpful folder (titled fitcontentassets). From here, you can easily have a look through and see if any seem out of the ordinary.

Optimising published lessons

When taking the decision to optimise a published lesson, you should be aware that any users who have already downloaded the lesson will have to re-download it. This is because when you upload make changes to content and re-save the lesson, Ed detects that there is a new version available, and will download it to replace the existing lesson. This could mean that shaving a few kilobytes off a lesson’s size by replacing an image triggers a new download of a megabyte or so, if the learner has already downloaded the old version of that lesson.

In cases where your learners have good internet connections, or your lessons are below 5mb, you don’t need to worry about triggering re-downloads. Similarly it may be that the savings you have made in optimising your lesson are significant enough that forcing new downloads for existing learners are worth it for the benefits to newly registered learners.

Have any questions about optimal file sizes? Send us a message on hello@edapp.com, and we’ll be sure to get back to you.