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.

1 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.

2 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 (=mp4a) 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.

3 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 (or at most 20) seconds is more than enough.

4 Encoder Settings

Video 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.

Video 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.

Video Bit Rate

For screen recording (FullHD, MP4, 20-25 ffps), a video bit rate of 8 Mbps is more than enough. 5 or 6 Mbps is probably good enough.

Audio Sample Rate

For a screen recording audio track (AAC = mp4a), a sample rate of 44100 Hz is good enough.

Audio Bit Rate

For a screen recording audio track (AAC = mp4a), a bit rate of 160 kbps is more than enough, 96 kbps is probably good enough.

5 Other Considerations

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 mouse cursor where a pointer device is being used (maybe even make the mouse cursor slightly larger). However, displaying mouse trails (which some software makes possible) is probably overkill.

No Watermarks

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

Hide the Recording Software UI

Do not leave the user interface of the recording software visible in your screen capture. There is always a way to hide it. If you have to start and stop the recording software, do that well in advance, so that it is not included in any video clips.

Use a Good Microphone

Use a good microphone. A headset microphone often produces better sound than a webcam mic or built-in mic. A professional streaming microphone is the best.

Make a Test Recording

Make a test recording. Make sure the audio is clear and loud enough. Make sure the font size is readable. Make sure the cursor is visible.

6 Tools by Platform

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

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. See my guide to Using OBS Studio. See also https://videohelp.com/software/Open-Broadcaster-Software.

  • Camtasia ($199 or 30-day free trial, but with watermark).
  • Morae (€2215 or 30-day free trial) used to be at morae.com. Morae was a product of TechSmith, but it was discontinued on 31 Dec 2019. The softare is still available for download at the Internet Archive. The 30-day free trial is full-featured and does not introduce watermarks into the videos. Great for capturing user test sessions. See my guide to Using Morae.

MacOS

Software packages:

Linux

Software packages:

Android

Software packages:

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

See also: https://maketecheasier.com/android-screen-recording-apps/

iOS

Built-in:

  • iOS (since 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 (on iOS 12 swipe down from the top right corner of the screen) and tap the Screen Recording symbol. There is a 3-second countdown.

      To also record the microphone, long press on the Screen Recording symbol, and then tap the Microphone symbol.

    • The status bar at the top display a solid red symbol 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 symbol on the status bar, then tap Stop).

See also: https://support.apple.com/en-gb/HT207935