Container Format
A file format that bundles one or more video, audio, subtitle, or metadata streams into a single file. Examples: MP4, MKV, MOV, AVI, OGG. The container is separate from the codec used to encode the streams inside it.
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A container format (also called a wrapper or multiplexer format) is a file type that packages different media streams together into one file. The container defines the file structure and how streams are stored and synchronised — but it does not determine how the audio or video is compressed. That is the codec's job.
Container vs Codec
A common confusion: people describe a file as "an MP4" when they mean an MP4 container with H.264 video and AAC audio. The same container can hold different codecs:
- MP4 file with H.264 video → standard streaming video
- MP4 file with H.265 video → smaller file, same container
- MKV file with H.264 video → same video codec, different container with more features
Common Container Formats
- MP4 — universal video container, widely supported
- MKV — flexible, multiple tracks, open-source
- MOV — Apple QuickTime container, used by iPhone and Final Cut Pro
- AVI — Microsoft's legacy container from 1992
- OGG — Xiph.Org's open-source container for Vorbis audio and Theora video
- WebM — Google's royalty-free container for VP8/VP9/AV1 video
Why Container Choice Matters
Different containers support different features:
- Multiple audio tracks — MKV yes, MP4 limited
- Embedded subtitles — MKV yes, MP4 limited, AVI no
- Streaming metadata — MP4 yes (moov atom at start), AVI no