Research and Development of a Near Real-time Captioning Service

Abstract

To broadcasting a live television program with a real-time closed captioning service, two sub-systems must be added to the existing broadcasting system: 1) a real-time speech transcribing module and 2) a live stream text receiving module. In this study, the technique called simulated-typing developed by National Electronics and Computer Technology Center (NECTEC) is used to produce real-time transcription for Thai. The PIMmala subtitle gateway and VT3 PEACH DVB-sub generator together are then used to produce closed captioning service from a live text stream in DVB-T2 format. From five technical experiments and two user experiments, it has been shown that the television broadcasting systems developed under this study can produce and broadcast a real-time closed captioning service that is acceptable by people with hearing disability which is the targeted group of this study. The captioning accuracies of live news programs are around 80-90%. In terms of delay, the caption appears on a television screen within 6.6 seconds after the corresponding speech. Due to bandwidth limitation, which the regulator allocated only 100 kpbs for the closed caption service, the caption has to be displayed in block of characters every 500 milliseconds which increases the delay.