11693.mkv.mp4 <480p>

In some cases, double extensions are used by malware to hide the true file type (e.g., file.mp4.exe ). However, since both .mkv and .mp4 are video containers, this is more likely a clerical or automated naming artifact. Numerical Prefix ("11693")

A file processed by a tool like Sonarr or Radarr where the ID corresponds to a specific entry in a movie/TV database. 11693.mkv.mp4

Many surveillance systems export clips using sequential numbering rather than timestamps. In some cases, double extensions are used by