A BDM file is used by different tools for different reasons and in video usage it often means Blu-ray/AVCHD BDMV navigation files—INDEX.BDMV or MOVIEOBJ.BDMV—that describe structure rather than store video, while actual streams are .m2ts/.mts under BDMV\STREAM and playback logic is defined by .mpls playlists and .clpi clip info, which explains why BDM files don’t open as videos; in backup contexts a .BDM may be a metadata index describing what was backed up and how large files are split or verified, usable only with its original backup program, and in other cases apps or games pack internal resources into .BDM archives readable only by their own tools.

The most reliable way to know what a BDM file is involves checking its context, because different systems reuse the extension: an SD-card or Blu-ray-like folder almost always signals BDMV/AVCHD metadata (with STREAM, PLAYLIST, .m2ts/.mts, .mpls, or .clpi nearby), a tiny BDM next to massive companion files indicates a backup catalog, and a BDM hidden in a game/app directory usually means app-specific resource data that needs its original software for viewing or extraction.

"BDM isn’t a single universal standard" means .BDM doesn’t define one global format because file extensions are just labels that different developers can repurpose, resulting in multiple unrelated meanings; a BDM in one environment may be Blu-ray/AVCHD metadata, another may be a backup index, and yet another may be application-specific data, so identifying it requires checking where it came from and what surrounds it rather than assuming one tool opens all BDM files.

For more information on BDM file opening software look at the web-site. A BDM/BDMV file typically appears in workflows built around Blu-ray or AVCHD structures, meaning it rarely stands alone and instead lives inside a BDMV directory with subfolders such as STREAM, PLAYLIST, and CLIPINF; in that layout the BDM/BDMV items serve as navigation and indexing rules while .MTS/.M2TS files in STREAM contain the real video, and the same structure emerges when Blu-ray discs are copied to a computer or when authoring tools output a Blu-ray/AVCHD project—so anything that resembles a disc export normally puts these files inside or beside a BDMV folder instead of giving you a single playable file.

Confirming a BDM file quickly means studying the files around it, because Blu-ray/AVCHD sets include a BDMV directory with STREAM, PLAYLIST, and CLIPINF and store real video as .m2ts/.mts; backup metadata appears as a tiny BDM next to huge multi-part chunks; and application data appears when a BDM sits among many odd program/game data files—so the simple rule is BDMV layout = Blu-ray/AVCHD, small + huge files = backup, all other cases = app/game.