  The growing need for instant spoken language transcription and translation is
driven by increased global communication and cross-lingual interactions. This
has made offering translations in multiple languages essential for user
applications. Traditional approaches to automatic speech recognition (ASR) and
speech translation (ST) have often relied on separate systems, leading to
inefficiencies in computational resources, and increased synchronization
complexity in real time. In this paper, we propose a streaming
Transformer-Transducer (T-T) model able to jointly produce many-to-one and
one-to-many transcription and translation using a single decoder. We introduce
a novel method for joint token-level serialized output training based on
timestamp information to effectively produce ASR and ST outputs in the
streaming setting. Experiments on {it,es,de}->en prove the effectiveness of our
approach, enabling the generation of one-to-many joint outputs with a single
decoder for the first time.
