The file won't open because the header (the first few bytes) is corrupted or overwritten with junk data.
Use exiftool to check for hidden strings in the "Comment" or "Title" fields. Pjmp4_at_Sape_mp4
Check the hex data after the free or moov atom. Often, flags are appended as plain text at the very bottom of the file. To provide a more specific write-up, could you share: The file won't open because the header (the
Open the video in VLC and frame-step (using the e key). Flags are often hidden in a single frame that lasts only 1/60th of a second. Pjmp4_at_Sape_mp4
Which or event this is from (e.g., HTB, TryHackMe, PicoCTF)?