Watching television/films in your target language is great, especially if you don't get many other oppotunities to hear it used in a normal setting. But don't just start learning a new language through this medium. Without knowing the language well enough it will just be too many hours of mainly babble, which is not effective. However, if you know the language well enough through other means, tv/film/auditory presentations are the best method to learn how to hear a language spoken fluently with understanding, assuming you will not be moving to a different country.
To learn a language, I recommend you learn the sounds and basic grammar, with just enough vocabulary to allow those activities. Just the basics here, like where adjectives go, how to form tenses, plurals, very common things. Do this online, or through books, and pick materials that appeal to you. If you stick to the basics like I recommend, this may take you only about a week. Just long enough to recognize the constructs, you don't need to be comfortable using them yet. Once you are comfortable with that, I recommend reading novels with a dictionary. Look up every word you do not know, don't worry about complex grammar or perfect understanding in the early stage, focus more on the vocabulary you can extract. Do this regularly as your primary language learning activity. Once you get to a point where you are reading with nearly full comprehension and only looking up rare or specialty words, switch to an auditory presentation, such as tv. Then engage in that medium regularly until you are understanding the vast majority of what it said. Both stages will take a large investment of time. It is a good idea to involve auditory from the beginning, but only make it your focus at the appropriate time.
This has worked for me. I adore language, expect to be fluent in a few before I die, and will continue to use this method. I am not yet fluent in Spanish, but I have read upwards of 5000 pages in it. Doing so gave me a mental feel for the language. I got to the point where my reading was smooth, nearly fluent, but my ability to process spoken Spanish was completely meager in comparison. I switched my primary language learning activity to television watching, and now I feel my ability to process spoken spanish is nearly as good as my reading. I simply cannot imagine what else would have improved my listening comprehension as well, save for a trip to a spanish speaking country where I then took up permanent residence.
So do I think it's effective? Yes, and without using something comparable, I believe it's necessary. Just don't focus on it too soon. And, a text book is only going to teach you so much. All language learning texts use a very narrow selection of vocabulary. You could read every textbook teaching your target language, master them all, and still be missing so very very much. So if you've covered a couple texts (or even much sooner), switch to reading with a dictionary. After all, grammar is a tiny tiny tiny matter compared to the almost never ending nature of vocabulary, and reading with a dictionary will generally expose you to even more grammar than a text. But even with all that, to learn to hear a language you have to expose yourself to it spoken. In that regard, tv is a perfect fulfiller of that experience, so, yes, tv in a foreign language is extremely effective. Just watch a variety of shows, including nature, medical, cooking, and more.