If you own a digital backup of the film and need external subtitle files (usually in .srt format), check major subtitle databases. Search specifically for "The Mayor of Casterbridge 2003" on:

(starring Ciarán Hinds) are available through both official streaming platforms and independent subtitle repositories. Official Streaming Options (Includes Subtitles)

Thus, when you search for these subtitles, you are not just trying to understand Ciaran Hinds' mumbling. You are participating in the preservation of Hardy’s linguistic world.