What ASC MHL is, and why your offload should write it
If you offload camera media, you’ve seen .mhl files appear next to your footage. Here’s what ASC MHL is, why it exists, and why your offload tool should write one for every job.
What an MHL is
MHL — Media Hash List — is a small XML file that records the checksum of every file in an offload, plus when and how it was copied. It’s a receipt for a card: a list of exactly what was moved and a fingerprint of each file, so anyone can later confirm nothing changed.
ASC MHL: the standard version
The American Society of Cinematographers turned this idea into an open standard, ASC MHL (the current, v2 generation). Standardising it matters for one reason: the manifest travels with the footage and can be read by any compliant tool. Post, a lab, a streamer’s QC department — none of them need your software, or even your brand of tool, to re-verify the media you handed over.
Why it matters on set
- Proof that travels. The checksums prove the copy that reached post is bit-for-bit the copy that left the card.
- No lock-in. Any ASC MHL-aware application can validate the files. You are never the bottleneck, and neither is any one vendor.
- Chain of custody. Production, post and insurance can all confirm the media is unaltered — which, when something is questioned months later, is the difference between a shrug and a claim.
Which tools write ASC MHL
As of 2026, ASC MHL is supported by Pomfort Silverstack, ShotPut Pro, YoYotta and Pomfort’s MediaVerify — and by Olycen, which writes ASC MHL v2 on every offload and includes it at the base price rather than behind a Pro tier. See how the tools compare.
Olycen and MHL
Every Olycen offload writes an ASC MHL v2 manifest alongside the media, using your choice of checksum algorithm (xxHash for speed, or MD5, SHA-256, C4 where a facility requires it). The same manifest is what lets Olycen — or anyone downstream — re-verify the footage long after the card is gone. See the features or join the beta.
Keep reading: Olycen vs OffShoot, ShotPut Pro and Silverstack · How to offload an SD card to multiple drives on Mac
Offload that never lies to you.
Olycen copies every card to as many drives as you want, verifies each file by reading it back, and only says the word verified once the proof is in. One-time $129, two Macs, no subscription — the launch list pays $99.