If you are looking for information on how to handle MP4 files generally:
The most specific reference to "9879" in a video context is a regarding a playback issue. 9879.mp4
: The "9879" in this context is part of the support article's unique ID ( d3a37253-2cf2-9879-7db6-9522f69b034c ) on the Microsoft Support site . Other Potential Meanings If you are looking for information on how
Outside of software troubleshooting, "9879" appears in various unrelated sectors: 9879.mp4
: MP4 files created in Windows 7 or Windows Server 2008 R2 may not play on non-Windows devices if they are longer than 429 seconds or stop unexpectedly after approximately 25 seconds.