Audio-Visual Speech-to-Speech Translation (AVS2S) typically prioritizes improving translation quality and naturalness. However, an equally critical aspect in audio-visual content is lip-synchrony—ensuring that the movements of the lips match the spoken content—essential for maintaining realism in dubbed videos. Despite its importance, the inclusion of lip-synchrony constraints in AVS2S models has been largely overlooked. This study addresses this gap by integrating a lip-synchrony loss into the training process of AVS2S models. Our proposed method significantly enhances lip-synchrony in direct audio-visual speechto-speech translation, achieving an average LSE-D score of 10.67, representing a 9.2% reduction in LSE-D over a strong baseline across four language pairs. Additionally, it maintains the naturalness and high quality of the translated speech when overlaid onto the original video, without any degradation in translation quality.

Despite recent advancements in speech processing, zero-resource speech translation (ST) and automatic speech recognition (ASR) remain challenging problems. In this work, we propose to leverage a multilingual Large Language Model (LLM) to perform ST and ASR in languages for which the model has never seen paired audio-text data. We achieve this by using a pre-trained multilingual speech encoder, a multilingual LLM, and a lightweight adaptation module that maps the audio representations to the token embedding space of the LLM. We perform several experiments both in ST and ASR to understand how to best train the model and what data has the most impact on performance in previously unseen languages. In ST, our best model is capable to achieve BLEU scores over 23 in CoVoST2 for two previously unseen languages, while in ASR, we achieve WERs of up to 28.2%. We finally show that the performance of our system is bounded by the ability of the LLM to output text in the desired language.

In the last several years, end-to-end (E2E) ASR models have mostly surpassed the performance of hybrid ASR models. E2E is particularly well suited to multilingual approaches because it doesn't require language-specific phone alignments for training. Recent work has improved multilingual E2E modeling over naive data pooling on up to several dozen languages by using both language-specific and language-universal model parameters, as well as providing information about the language being presented to the network. Complementary to previous work we analyze language-specific parameters in the attention mechanism of Conformer-based encoder models. We show that using language-specific parameters in the attention mechanism can improve performance across six languages by up to 12% compared to standard multilingual baselines and up to 36% compared to monolingual baselines, without requiring any additional parameters during monolingual inference nor fine-tuning.