Container format
Also known as: media container, wrapper format, file container
A container format is the file wrapper that packages compressed video, audio, subtitles, and metadata into one file — for example MP4, MOV, or MKV. It defines how the parts are stored together, not how they are compressed; the codec inside does that.
- Wraps video, audio, subtitles, and metadata into one file
- MP4, MOV, and MKV are common containers
- The codec inside, not the container, controls size
What a container does
A container is the outer box around your media. It bundles the encoded video stream, one or more audio tracks, subtitles, chapters, and metadata, and tells a player how to keep them in sync. The file extension — .mp4, .mov, .mkv — names the container.
It does not compress anything itself. The actual shrinking is done by the codec stored inside, which is why the container alone tells you little about a file’s size or quality.
Common containers and compatibility
MP4 is the universal choice that plays almost everywhere. MOV is Apple’s native QuickTime container and the iPhone recording default. MKV is the flexible open container favored for movies but unsupported natively on iOS.
Converting between containers (re-wrapping) is fast and changes compatibility without re-compressing. To actually reduce file size you have to re-encode with a more efficient codec, which is a separate, slower step.