The "source" prefix typically indicates that this is the original, high-quality version of the upload before it was compressed into different resolutions (like 720p or 480p) for streaming. The "NI" could refer to a specific server node, a "No Index" flag, or a proprietary internal tag.

If you have this file and cannot open it, or if it lacks metadata: How to play MP4 files in Windows - Microsoft Support

This alphanumeric string is almost certainly a hash or a unique content ID. Platforms like Twitch, YouTube, or Facebook use these to prevent file overwrites and to manage massive databases where simple titles would lead to collisions.

When downloading clips from Twitch, the platform often provides files with random alphanumeric names or weird adjective-noun combinations to ensure uniqueness.

Some sites use these names to obfuscate content and prevent users from easily guessing the URLs of other private videos. How to View or Manage the File

Files with these types of "word salad" or hashed names are commonly found in the following contexts:

When you "Inspect Element" on a site like Instagram or Facebook to find a video's direct source, the resulting filename is often a long hash like this.