  Watching movies and TV shows with subtitles enabled is not simply down to
audibility or speech intelligibility. A variety of evolving factors related to
technological advances, cinema production and social behaviour challenge our
perception and understanding. This study seeks to formalise and give context to
these influential factors under a wider and novel term referred to as Dialogue
Understandability. We propose a working definition for Dialogue
Understandability being a listener's capacity to follow the story without undue
cognitive effort or concentration being required that impacts their Quality of
Experience (QoE). The paper identifies, describes and categorises the factors
that influence Dialogue Understandability mapping them over the QoE framework,
a media streaming lifecycle, and the stakeholders involved. We then explore
available measurement tools in the literature and link them to the factors they
could potentially be used for. The maturity and suitability of these tools is
evaluated over a set of pilot experiments. Finally, we reflect on the gaps that
still need to be filled, what we can measure and what not, future subjective
experiments, and new research trends that could help us to fully characterise
Dialogue Understandability.
