What is the purpose of Media Atom 'flags' within the QuickTime videos, I see for the most part they are set to zero but what does this achieve?

Documentation I am reading is the following: https://developer.apple.com/library/mac/documentation/QuickTime/qtff/QTFFChap2/qtff2.html

2 Answers 2


They are a type of metadata specific to the QuickTime container. They can contain all kinds of extra information for the video player to read out and use.

QuickTime movie atoms have an atom type of 'moov'. These atoms act as a container for the information that describes a movie’s data. This information, or metadata, is stored in a number of different types of atoms. Generally speaking, only metadata is stored in a movie atom. Sample data for the movie, such as audio or video samples, are referenced in the movie atom, but are not contained in it.


The Media Atom object does not have a Flags field, but the Media Header Atoms does:

Flags - Three bytes of space for future movie header flags.

In which case it's basically say, these values are reserved for future use, and presently are just byte alignment packing.

In most RFC's these area's are called Reserved as compared to flags.

This would explain why they are zero, as by the spec, they should be set zero, so in the future none zero value can be interpreted to mean "something".

If I'm mistaken the section you refering let me know.

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