CMML File

What are CMML files and how to open them

Are you having problems opening a CMML file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CMML files.

What is a CMML file?

A .CMML file is a Continuous Media Markup Language file.

Continuous Media Markup Language is an XML-based way to describe audio or video that adds structure and metadata so that continuous media can be indexed, annotated, searched, and linked much like text documents. It is most often used with Annodex, a framework for handling time-continuous data such as audio/video, where CMML describes clips, metadata, hyperlinks, and other information tied to specific times in the media.

Files in this format are authored (written) by tools or users creating Annodex content or preparing timed annotations for media streams. They are read by media players or web systems that support Annodex and CMML, which use the markup to display subtitles, captions, descriptive text, hyperlinks for temporal anchors in the media, and metadata like titles or producers. This format integrates with streaming workflows by allowing the annotations to be interleaved with media data (in Annodex streams) so synchronization between visuals/audios and text or other metadata is preserved.

CMML documents begin with a "stream" element (optional) to declare media source(s), include a "head" section that holds metadata about the whole media resource (such as title, author, language), and then contain one or more "clip" elements that each cover a time interval ("start" and possibly "end" attributes) and may include tags like desc (description), caption, or a to hold captions or hyperlinks that target that clip.

Files produced in this format can be recognized by their XML structure: they begin with a less-than sign at the start, include tags "cmml", "stream", "head", "clip", and contain the keywords "DESC", "START", etc. Signature bytes include 0x3C at offset 0, 0x6D6C at offset 3 (for "ml"), and the presence of strings like CMML, STREAM, START, DESC, HEAD.

How to open CMML files

Important: Different programs may use files with the CMML file extension for different purposes, so unless you are sure which format your CMML file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 31, 2026

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about CMML file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.