Enhancing Neural Speech Coding with Semantic and Visual Cues
At low bitrates, neural speech codecs have limited capacity to encode all information needed for high-quality re construction, especially when relying solely on speech-derived representations. To address this limitation, this paper proposes a Semantic- and Visual-enhanced Speech Codec (SVSC), which in corporates semantic and visual cues into the neural speech coding process. Specifically, built upon a mainstream neural speech cod ing architecture, SVSC introduces a semantic encoding-decoding branch and an image analysis-synthesis branch. It fuses deep semantic features with visual cues through a cross-attention mech anism, forming an auxiliary high-level representation enriched with contextual and articulatory information. To handle different inference scenarios, SVSC introduces two information-injection strategies based on the availability of auxiliary semantic and vi sual cues. When such cues are available, the fusion mode directly incorporates the auxiliary representations into the speech coding branch through feature concatenation; otherwise, the distillation mode transfers auxiliary information into the speech coding branch through knowledge distillation during training, enabling speech-only inference without additional inputs. Experimental results validate the effectiveness of incorporating semantic and visual cues, improving the ViSQOL score of reconstructed speech from 3.86 to 4.01.