The second half of the name ( 421b70fb7... ) is a hash . If you possess the original file, you can verify its integrity by running a checksum; if the hash changes, the file has been edited or corrupted.
Websites or apps that rip content from YouTube, Instagram, or Pinterest often assign these alphanumeric strings as unique IDs for the downloaded files. Key Features of this File Type 3156512-421b70fb79abfe4fae3d57cb8c15192e.mp4
If you are looking for the source of the video , please describe the content (e.g., what happens in the video), and I can help identify the original creator or platform. The second half of the name ( 421b70fb7