mmMovermmMover › ASC MHL
ASC MHL, explained by a DIT
ASC MHL is the American Society of Cinematographers standard for recording the checksums and copy history of media files. It lets post, the lab or an archive prove that their files are the files that came off the camera.
What mmMover writes
Next to the media on every drive, mmMover creates an ascmhl folder: one .mhl file with the checksum of every file (xxHash64, optionally MD5) and ascmhl_chain.xml, the chain of generations.
Appending new clips from the same card, or copying failed files again, adds a new generation instead of rewriting history. Files that failed are recorded as failed, never as copied.
Verifying a backup later
- In mmMover: Verify backup reads every file and compares it with every generation of the ASC MHL, then writes a verification report.
- With the
ascmhlcommand-line tool from the ASC. - In Silverstack, ShotPut Pro and other MHL-aware tools.
Why xxHash64
It is many times faster than MD5 and catches damaged or missing data just as reliably, so the checksum is never the bottleneck of an offload. When a production asks for MD5, mmMover writes both.