The prefix indicates that this is a temporary filename generated by a messaging app—most likely Facebook Messenger. cm : Likely stands for "Content Manager" or "Chat Media."
Because filenames like this are generic, they are sometimes used to disguise malicious files in phishing emails. cm-chat-media-video-1367f1c09-0d27-.mov
: Your device automatically cached the file so it could play within the messaging app. The prefix indicates that this is a temporary
How did you , and what are you trying to do with it? cm-chat-media-video-1367f1c09-0d27-.mov