Studies into the role of audiovisual input and captions (i.e., subtitles in the same language as the audio) for L2 learning have shown that such input can positively influence L2 learners' acquisition of lexical items. Few studies have explored the effects of captioning on learners' capacity to segment the speech stream. This study investigates the effects of watching an episode of a Spanish TV-series (72 minutes) on speech segmentation among 37 (low-) intermediate L2 learners of Spanish in a captioned (n = 12), uncaptioned (n = 14), and control (n = 11) group. One week before the treatment, participants completed the LexTALE-ESP vocabulary size test. They also took a pretest-posttest shadowing task, which measures learners' ability to repeat back sentences. It included 20 treatment, 20 related (i.e., from the same TV-series as the treatment), and 20 unrelated (i.e., another TV-series) sentences presented in auditory or audiovisual input mode. Linear mixed-effects models revealed that watching video contributed to learners' speech segmentation, irrespective of captioning presence. Shadowing task performance improved significantly on treatment and related but not on unrelated sentences. In addition, shadowing task performance was positively influenced by learners' vocabulary size. Input mode of the shadowing sentences did not influence posttest performance.