A: MKV (Matroska) with an AC3 or E-AC3 audio track. MP4 can also support 5.1 but less commonly.
Platforms like the Internet Archive host thousands of classic films (pre-1928) and indie shorts. While not all offer 5.1, many preservation projects have re-encoded films with surround sound. Search for “AC3” or “5.1 surround” within the archive. dolby digital 51 movies hot free download
A: Search for “Dolby Digital 5.1 channel test” on the Internet Archive – there are several free test tone files in AC3 format. A: MKV (Matroska) with an AC3 or E-AC3 audio track