Video Containers and Codecs Explained

The extension tells you the package. It does not tell you everything needed to play the file.

Containers: MKV, MP4 and WebM

A container packages media tracks and metadata. Two files with the same extension can contain different video and audio encodings.

Codecs: H.264, H.265, AV1 and VP9

A codec encodes or decodes a media track. A browser must support the relevant decoder to play it. Device capabilities also affect whether decoding and encoding are available.

Remuxing versus encoding

Remuxing moves compatible encoded tracks into a different container. Encoding creates a new compressed stream. FreeMediaEditor can prepare some MKV inputs by remuxing, but exporting an edited timeline re-encodes the picture.

When a file will not open

Try a current Chrome or Edge browser and a short sample. If the codec cannot be decoded, use a compatible source. Renaming the extension does not convert the media.

Reference: MDN media container guide.