Downloading the audio is only half the battle. You now need to (combine) it into your video file. Here is the professional workflow using free software.
Surprisingly, many classic films (pre-1928) are in the public domain. Websites like host full movies where you can download individual MP3 or M4A audio tracks. Where To Download English Audio Track For Movies
: A massive digital library where you can search for movies and radio recordings by language. By using ISO language codes (e.g., "en" for English), you can find historical audio, newscasts, and feature films. ListenToAMovie.com Downloading the audio is only half the battle
Ensure your TV or player supports the audio format. AC3 (Dolby Digital) is the most compatible, while DTS or TrueHD might require specific sound systems. Surprisingly, many classic films (pre-1928) are in the
ffmpeg -i movie.mp4 -i english_track.ac3 -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 -async 1 -shortest output_synced.mp4