The "source" suffix in the filename might imply that a specific frame contains the key.

Look for unusual entries in the "Comment," "Description," or "Artist" fields. Creators often hide strings or Base64-encoded text here.

The MP4 might be a "polyglot" or have a ZIP/RAR file appended to it. Tool: binwalk Command: binwalk -e 0h8q1ak2acptoechqhoxq_source.mp4

The first step in any file-based challenge is checking the metadata. Tool: exiftool Command: exiftool 0h8q1ak2acptoechqhoxq_source.mp4