Answered for language learning in general. No specific language was set for this question, so the findings are drawn from general second-language research rather than one language’s literature.
The evidence suggests subtitled video is generally more helpful for listening comprehension than pure audio alone, especially when the subtitles are in the language you're learning (not translated into your own). But the details matter: translated (native-language) subtitles can actually block listening gains, watching with sound off and subtitles alone hurts comprehension, and how much subtitles help depends on your proficiency level and how actively you engage with them rather than just having them on screen.
In a study where English learners watched a TV episode either with English (same-language) subtitles, Spanish (translated) subtitles, or no subtitles, listening comprehension improved most for the English-subtitle group (a 17% gain), less for the no-subtitle group (7% gain), and not at all for the Spanish-subtitle group.6
A large study using full-length TV episodes found that captions (on-screen text in the same language being learned) improved comprehension especially in early episodes and in episodes that were more difficult, suggesting captions matter most when learners are struggling.7
A study of 150 learners of Spanish, Russian, Arabic, and Chinese found that watching captioned videos produced consistently higher comprehension test scores than watching the same videos without captions, across all four languages and both proficiency levels tested.4
When given a choice between clickable subtitles and a full transcript as help while completing a listening activity, learners opened and used subtitles far more often than the transcript, but overall more than half of the times learners opened a help option, they didn't actually engage with it (they clicked through without really reading or using it).1,11
Eye-tracking research found that even quite fast subtitles (up to 20 characters per second) did not reduce viewers' comprehension scores compared to slower subtitle speeds, suggesting viewers can keep up with typical subtitle reading demands.5
A large eye-tracking study found that watching subtitled videos with the sound turned off (relying on text alone, not audio) led to worse comprehension, higher mental effort, and less enjoyment compared to watching with sound on, even though many viewers do this deliberately.12
In plain terms
In a study of young language learners, adding audio to an on-screen story (so they read text while also hearing it) allowed them to look at the accompanying pictures more, and spending more time looking at those pictures was linked to better comprehension, while spending more time reading the text alone was linked to worse comprehension.3
In a controlled comparison, a group of intermediate English learners who watched subtitled films alongside structured lesson activities showed notably larger gains in listening comprehension than a group taught with a traditional textbook-only curriculum.2
Surveys and interviews with EFL and ESL university students in several countries (Turkey, Bangladesh, Indonesia) consistently found that learners believe subtitles help them understand dialogue, learn vocabulary, and connect spoken and written language, though they also report struggling with fast dialogue, unfamiliar accents, and difficult vocabulary even with subtitles on.8,9,10
A year-long study of teenage learners watching subtitled or captioned TV series found that vocabulary gains occurred under all subtitle conditions, but learners who already had higher proficiency before the study gained more from the viewing, suggesting subtitled input helps everyone somewhat but benefits more advanced learners more.13