If the file is truncated (didn't finish downloading), you can try using a tool like Handbrake to "re-encode" it into a fresh MP4 file.
A lightweight alternative for Windows users. IINA: A modern, sleek player for macOS users. 3. Troubleshooting Playback Issues espl1080.mkv.mp4
If the file won't open in standard players (like Windows Media Player or QuickTime), use a "universal" player that handles high-definition 1080p content and various containers: If the file is truncated (didn't finish downloading),
The filename appears to be a video file that has been double-extended or incorrectly renamed. Usually, this happens when a high-definition (1080p) video in an MKV container is converted or renamed to MP4 for better compatibility. 1. Fix the Filename espl1080.mkv.mp4