Video Compression (with specific reference to Powerpoint slideshows)

Illustration by Cayla Basson

This article gives a very quick tutorial on video compression. With online teaching becoming a norm during the lockdown, the unavailability of good internet access has emerged as a major stumbling block for people in many parts of the world. This tutorial would be particularly useful for people who would like to upload a smaller (in terms of size) version of their lecture to make it available to students on the other side of digital divide. The tutorial focuses on powerpoint presentations with slide-wise narration.

The COVID-19 crisis has meant that learning institutions must move their content online. Many of us will be using video content, and may be concerned with the size of the files students must download. I work in the physics department at Stellenbosch University, and in the South African context, we need to be aware that many students will not have access to fast or reliable wi-fi.

This quick, 1 minute tutorial shows a very basic technique to compress video files (i.e. reduce the file size) using a freely available software called Handbrake. Many videos can be significantly compressed with negligible loss of quality. This is particularly true for narrated Powerpoint presentations that have been exported as videos. Here is an idea of the numbers:

2 MB:      (.pptx) 20 slide Powerpoint presentation
20 MB: (.pptx) or (.ppsx)  20 slide Powerpoint presentation with 15 min narration and annotation
70 MB:    (.mp4) exported as 15 min video
15 MB:     (.mp4) video compressed with negligible loss of quality

Remember that if you are exporting narrated Powerpoint presentations as video, select the lowest quality.

  • “File” “Export”  “Create a Video”
  • Do not export as Full HD (1080p). Click on the down arrow and select “Standard 480p”

Compressing the video

  • (For a once-off compression, use one of the many easy-to-use online versions such as Clideo)
  • Handbrake ( is an excellent free compression software you can download onto your computer.
    (It might request additional downloading of Microsoft add-ons)
  • Select “Open Source” and upload the video file you wish to compress
  • From the subheadings select “Video” (Full screenshot below)

    Select Avg Bitrate (kbps) and enter your preferred bitrate. A bitrate of 100 kbps will compress the video to approximately the same size as the original .pptx file. A compression to 50 kbps will still result in a negligible loss in quality

  • Now select “Audio” (Full screenshot below)

  • Select the lowest possible bitrate (64 kbps)

  • Now click “Start Encode”. This will create a .mp4 video file.

Figure 1: Screenshot of video compression
Figure 2: Screenshot of audio compression

Here are a few additional tips for recording narrations in a Powerpoint presentation.

Recording Slideshow (Adding Narration and Annotations)

  • Click on “Slide Show” and then select “Record Slide Show”.
  • Narrations are saved to a particular slide. If you advance to the next slide, the subsequent narration will be saved to that slide.
  • To redo the narration for a particular slide click “Record Slide Show” and then choose “Record from Current Slide”. Click “Record” to record over previous narration. Make sure you press STOP before you advance onto the next slide, otherwise you’ll continue to record over previous material.
  • Unfortunately APPLE devices (e.g. IPads) are not compatible with narrations (.pptx) on Powerpoint. Visual annotations (e.g. drawing) can be done on a laptop or desktop with WACOM drawing pad (connects via USB) or similar.

Other Tips  for Powerpoint presentation with audio narration.

  • You can also share the .pptx file, and students can watch the slideshow in powerpoint. (This way they also have the individual slides).
  • Pressing “s” pauses the presentation! (All other keys advance to the next slide!) This is important if you wish to include concept tests in your presentation. For example, if you have a slide that poses a problem, with the solution on a forthcoming slide, your narration might be as follows: “Here is a problem for you to try. Pause the presentation by pressing ‘s’ now. Don’t immediately look ahead to the next slide for the solution!” OR “There is a lot of text on this slide. Pause the presentation by pressing ‘s’, and carefully read through all the text on the slide. Press ‘s’ again when you are ready to continue with the narration.”

Philip Southey

Contact Philip with queries (

Illustration by Liani Malherbe

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