Now that a Web Audio API is available for THEOplayer (from version 2.19.4 onward), it is also possible to add a peak limiter to the audio. This can be useful when there are big differences in volume. For example, an ad in the middle of a video that is much louder than the video itself, but also differences between two subsequent videos, or even within one video.
An example of the latter is shown in this demo. Here, the same video is shown twice. One is without a peak limiter on the audio, and once with a peak limiter included. Around the 26th second, there is a big change in volume, which shows the usefulness of the peak limiter.
The open-source peak limiter that was used for this demo can be found on GitHub (https://github.com/tcarpent/PeakLimiter).