Need Expert to Fix Large MP4 Video File Not Playing Anywhere

I have recorded a video (MP4 format) around 15GB in size.
The file is not playing on any media player (PC or mobile).

I need an experienced video expert who can:

Diagnose the issue (corrupted file / codec problem / incomplete recording)

Repair or recover the video file

Make it playable without quality loss (if possible)

Optionally compress the file to a smaller size

Details:

File size: Approx. 15GB

Format: MP4

Recorded recently

Currently not opening in standard media players

Please apply only if you have experience in:

Video repair

Large file recovery

Codec fixing

Professional video tools

Let me know:

What tools you will use

Estimated time to fix

Previous similar work (if any)

Looking for quick and reliable solution.

Thank you.