The suffix refers to the MPEG-4 Part 14 multimedia container format. It is the most common format for digital video storage and streaming because:
If you encountered "19353.mp4," it is likely from one of the following: 19353mp4
It offers a high degree of compression while maintaining visual quality, making it ideal for the types of digital repositories where "19353" would be stored. The suffix refers to the MPEG-4 Part 14
The file is frequently linked to the title The Last Man (likely the 2018/2019 film starring Hayden Christensen, though it can refer to several films with this title depending on the specific archive). You may have found a folder or server
You may have found a folder or server where movies are listed by ID numbers.
Many streaming services use these numerical identifiers in their .m3u playlists to link to a back-end server.