A .CMV file is most often connected to video but varies across systems, so its meaning comes from the source: CCTV/NVR/DVR exports use proprietary structures readable only by their tools, older or niche cameras may produce odd wrappers, and a folder containing partner files (.idx, .dat, .db, numbered pieces) often means the CMV is just one part of a larger set; use file size to guess whether it’s index vs. footage, try MediaInfo to detect real codecs, test VLC for partial compatibility, inspect hex signatures to spot MP4/AVI/MKV markers, and rename a copy to .mp4/.avi/.mpg when the extension seems incorrect.

When I say a CMV is "a video file," I mean it includes timed sequences rather than raw frames, since a typical video holds a video track, maybe an audio track, timestamps for synchronization, metadata like frame rate and resolution, and occasionally subtitle tracks; the container (MP4, MKV, AVI) defines the structure, and the codec (H.264, HEVC, VP9, AAC) defines how the media is encoded, so two "videos" can act very differently, and a CMV might contain valid streams but still fail to open if its container or codecs aren’t broadly supported.

Some CMV files break playback or seeking because the container uses vendor-specific timestamp logic, so players can’t navigate the timeline despite having valid video inside; DVR/NVR workflows often require the manufacturer’s player to interpret chunked recordings and external index files before exporting to MP4, and this highlights that "video file" means time-based media, not automatic compatibility, with many CMVs relying on proprietary layouts and folder-dependent partner files that, if moved or missing, render them unplayable.

Another reason CMV files fail is that some use nonstandard codecs that built-in players don’t support, so even if the container is partly readable, the player lacks the decoder and throws a generic "can’t play" error; some security/camera systems also add authentication to prevent easy copying, making the file appear meaningless until opened through the vendor’s tool, and other systems delay writing a full seek index or store it separately, causing general players to stutter or only play from the beginning—so CMVs often misbehave not because they lack video, but because their packaging, indexing, and protection don’t follow standard media rules.

When a CMV isn’t a "normal video," it means the file doesn’t contain the whole audiovisual stream, common when CMV acts as a map/index that references footage stored elsewhere or as a segment of a multi-piece recording, often depending on other local files and occasionally pointing to encrypted/proprietary streams—so it’s necessary for system playback but not intended to function as a standalone video file.