This paper introduces a novel, completely automatic, audio-subtitle synchronization algorithm designed to increase the accessibility and comprehension of the hearing-impaired people over the video documents. The major contribution of the paper involves the anchor words matching strategy that can reliably put in correspondence the subtitle document generated by a human transcriber and the automatic speech recognition (ASR) textual file. In addition, we propose a subtitle positioning strategy that automatically determines the optimal location for each phrase on the user screen, with respect to the video semantic content. The experimental evaluation validates the proposed method with average accuracy scores superior to 90%.