HCI Practicals: Session Capture

Session Capture

Session capture refers to the recording of a test or evaluation session on the device itself. Some software is capable of recording webcam video and audio streams (and even mouse click events and browser URLs) in addition to screen contents.

Lossless or Lossy

A lossless video codec, such as TechSmith Screen Capture Codec (TSCC) for Camtasia or Morae, or CamStudio Lossless Codec for CamStudio will give the best visual quality (individual pixels are preserved as-is), but will generally result in huge video files. High-quality lossless screenshots can be extracted later and saved as PNG format.

Using a lossy video codec, such as H.264 used in MP4, produces much smaller files, but also introduces artefacts into the video (and any still frames later extracted) due to the compression scheme. However, for the purposes of usability evaluation, a lossy codec is often sufficient. If the original screen recording uses a lossy codec, it is reasonable to extract still frames as JPEG (.jpg) format (at the same resolution and with a reasonably high quality setting where available).

File Format

For use on the web, a video format widely supported by web browsers should be used. Currently, MP4 with H.264 video and AAC audio is the most widely supported, followed by WebM. See the detailed information on formats supported for the HTML5 audio and video elements at https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats.

There were some licensing issues regarding the use of H.264. However, the licensing authority (MPEG LA) announced in 2010 that it will never charge royalties "for internet video that is free to end users".

WebM was initiated by Google to be a patent-free open source alternative. It uses the VP8 or VP9 video codec and the Vorbis or Opus audio codec.

Resolution

FullHD video (1920×1080 or 1080×1920) produces huge file sizes. For use on the web, limiting the video resolution to 720p (1280×720 or 720×1280) can sometimes be a reasonable trade-off between quality and file size.

Frame Rate

For screen recording, 25 frames per second is more than enough. If the recording software allows, 20 fps or even 15 fps is probably good enough.

Mouse Cursor and Touch Points

When recording on a touch device, it can be useful to visually display touch events. The same is true for the cursor where a pointer device is being used. However, displaying mouse trails (which some software makes possible) is probably overkill.

Video Clip Duration

When extracting or creating individual video clips, make them long enough to show the issue, but no longer. For most usability findings 10 to 15 seconds is more than enough.

Archiving vs Dissemination

One strategy is to make complete session recordings in high quality (lossless, high resolution, but huge files sizes) for archival purposes. Screenshots and video clips can be extracted later. Individual video clips can then be converted down to, say, 720p MP4 for inclusion in a web-based report or for dissemination.

Watermarks

Some free or trial versions of software leave a watermark (visible imprint) on the video that is recorded. For the HCI practicals, do not use recording software which leaves watermarks in the video!

Tools by Platform

The following subsections list some of the tools which are available for each platform.

1 Microsoft Windows

Software packages:

  • OBS Studio (free). Free and open source, for Windows, macOS, and Linux. Can combine multiple input video and audio signals and record (or stream) them.
  • Morae (€2215 or 30-day free trial). The 30-day free trial is full-featured and does not introduce watermarks into the videos. Great for running user tests. See my guide to using Morae.
  • Camtasia ($199 or 30-day free trial, but with watermark).

If you use Windows, I highly recommend that you download and use the (free) trial version of Morae.

2 MacOS

Software packages:

  • OBS Studio (free). Free and open source, for Windows, macOS, and Linux. Can combine multiple input video and audio signals and record (or stream) them.
  • QuickTime Player (free, pre-installed).
  • Silverback (£29 or 30-day trial, but with watermark).
  • Camtasia ($199 or 30-day trial, but with watermark).

3 Linux

Software packages:

  • OBS Studio (free). Free and open source, for Windows, macOS, and Linux. Can combine multiple input video and audio signals and record (or stream) them.
  • vokoscreen (free). The huffyuv enocder is lossless, the libx264 encoder produces H.264/MPEG-4 AVC streams.

4 Android

Software packages:

  • AZ Screen Recorder (free). In the settings, it is possible to turn on the visual display of touch events.

5 iOS

Built-in:

  • iOS version 11 contains built-in functionality to record the screen:
    • Screen Recording must first be enabled (added to the Control Center): Settings → Control Center → Customize Controls, then tap the + symbol next to Screen Recording. The Screen Recording symbol is a solid circle with a circle around it.
    • To record the screen, open the Control Center (swipe up from bottom) and tap the Screen Recording symbol. There is a 3-second countdown.
    • The status bar at the top turns red during recording.
    • It is not (yet?) possible to turn on display of touch events.
    • To stop recording, open the Control Center and tap the Screen Recording symbol again (or tap the red status bar, then tap Stop).

Other suggestions for capturing screen video on iOS devices are here: https://apptamin.com/blog/capture-iphone-ipad-screen-video/