Standard players (like Windows Media Player) often struggle with .mkv or FLAC audio.
This file appears to be a high-quality of episode 24 of the anime Nagi no Asukara (A Lull in the Sea), released by the fansub group [FFF] . Technical Specifications Resolution: 1080p (Full HD). Audio: FLAC (Lossless audio, highest quality). Source: Blu-ray Disc (cleaner image than TV broadcast). [FFF] Nagi no Asukara - 24 [BD][1080p-FLAC][0FC...
Explaining the if you've already watched it. Standard players (like Windows Media Player) often struggle