There are many public domain movies on YouTube. Most of them are available in English. To download copyright-free movie audio tracks from YouTube, you can subscribe to YouTube Premium, download the movie and convert it to MP3.
Internet Archive is a digital library with a large collection of free movies, books, audio files, images, etc. You can also find movie audio tracks in this website or download movies in MP3 format. To find the movie audio track, type the movie title in the search field, open it and click MP3 under the DOWNLOAD OPTIONS.
A great source for German movies and series is the ARD Mediathek. You can download the app for tablet or phone for free. Many of the series and movies are available outside Germany but some are not. For instance, in France, where I live, you cannot get Der Tatortreiniger on Prime but it is available for free on the ARD Mediathek. All the Tatort series too. Also ZDF Mediathek is similar. The second German tv channel. 2b1af7f3a8