I got Spring Boot application running on Heroku server and mp4 file on AWS S3 storage. Filename of that mp4 is in database on Heroku.
I am using thymeleaf to get data. Developer console shows no error, but I can see only the player with all buttons (configured in js file)

        <div class="player">
            <video class="video-container" controls>
                <source th:src="@{/files/{filename}(filename=${product.imagePath})}" type="video/mp4"/>
                <source th:src="@{/files/{filename}(filename=${product.imagePath})}" type="video/webm"/>
                <p>No HTML5 vid supported</p>
            </video>
            <div class="controls">
                <div class="progress">
                    <div class="progress__filled"></div>
                </div>
                <button class="controls__btn playPauseBtn" title="Toggle Play">
                    ►
                </button>
            </div>
        </div>

@RequestMapping("/productvid")
@Controller
public class ProductDetailsControllerVid {

    @Autowired
    private ProductService productServiceImpl;

    @GetMapping("/{id}")
    public ModelAndView getDetails(@PathVariable("id") Long id){
        if (id == null || id <0)
            return redirect();
        else {
            try {
                Product product = productServiceImpl.findById(id);
                ModelAndView mav = new ModelAndView("product/detailsvid");
                mav.addObject("product", product);
                mav.addObject("comment", new Comment());
                return mav;
            } catch (ProductNotFoundException e) {
                return redirect();
            }
        }
    }