Wrapper format

Definition
A wrapper format is a

"[d]igital file format designed as an envelope for one or more streams of related digital content, where the stream format is specified independently."

Overview
"For example, the QuickTime format is a wrapper that typically contains audio or video bitstreams, which may conform to one of many compression encodings. In contrast to bundling formats, files compliant with a wrapper specification are typically used as is by a reader/player that understands both the wrapper and the encoding of encapsulated bitstreams."