Container Format
Definition
A file format (MP4, MKV, MOV, AVI, MXF) that multiplexes video, audio, and metadata tracks into a single file with a defined byte structure. The container handles synchronisation and seeking; it does not define how the media is compressed.
- Field
- Video and audio file structures
- Examples
- MP4, MKV, MOV, AVI, MXF
- Function
- Multiplexes video, audio, metadata tracks
- Handles
- Synchronisation and seeking
- Does not define
- How the media is compressed
Common questions
Why can the same container hold video encoded with completely different codecs?+
The container only defines the byte-level packaging, track indexing, and timing information, leaving the actual compression scheme to whichever codec was used to encode each track, such as H.264 or H.265 for video and AAC or MP3 for audio. This is why a media player can open an MP4 file but still fail to play it if it lacks the specific codec the file uses.
Why does an examiner need to identify both the container and the codec separately?+
The container reveals structural metadata such as creation timestamps and track layout, while the codec determines what compression artefacts, frame structure, and potential re-encoding signatures are present in the actual media data. Authenticity analysis, such as detecting a re-encoded or edited video, generally depends on the codec-level evidence rather than the container alone.
Related terms
- Codec
- A coder/decoder algorithm that compresses and decompresses media data. H.264/AVC and H.265/HEVC are the dominant video codecs; AAC and MP3 are dominant...
- GOP (Group of Pictures)
- The repeating sequence of I, P, and B frames in an inter-frame compressed video. GOP size (the distance between I-frames) is an...
- I-Frame
- An intra-coded frame: a self-contained image compressed without reference to any other frame, like a JPEG. I-frames are the only random-access entry...
- Perceptual Coding
- Lossy compression that exploits psychoacoustic or psychovisual masking to discard information the human senses are least sensitive to. MP3, AAC, and AC-3...
- Rewrapping
- Moving a compressed bitstream from one container to another without decoding it. Forensically equivalent to the original encoded stream; no new generation...