If your goal is to have students engage with the language, subtitles can distract their attention. If, however, you want your students to focus on a cultural aspect of the film, then it may be appropriate to use subtitles. If the focus is language, though, consider this format for guiding your students through the process of understanding the language that they are hearing.
The basis of this teaching method is the development of schemata. Schemata is simply the link between all thoughts and concepts on a topic that we as humans possess. For example, we think of the word “house,” but this word does not exist in our brain in an isolated vacuum. Rather, along with house, we have an entire web of concepts connected to it that we understand. We know that: we live in a house, a house has rooms, the rooms have names, we do particular things in each room, house are located in particular places, certain people live in houses, etc. All of this information connected to the idea of a “house” is a schemata.
When teaching students to comprehend language, it is important to explicitly teach them to access their schemata on the topic that they are listening to. When watching a video, it is helpful to have students watch a scene three times. Perhaps you could do this with a few scenes in a movie rather the the entire movie. Here is what happens during each viewing:
Students should watch the scene (about 1-2 minutes long) without the sound. During this viewing, students should focus on the visual aspects of the scene. When the scene is done, students quickly list everything that they saw in the target language and make a hypothesis about the what is happening in the scene. Based on this hypothesis, students should write down 5-10 words that they expect to hear.
During the second viewing, students should watch with sound and circle any words that they wrote down that they hear. They will quickly see that they understand more because they have accessed the schemata around the topic.
Students should watch the scene with sound and no notes, during which they should understand much of the language, without having been given words by the teacher. Rather, they are using their own intuition.
HERE are some movie exercises that follow this process.