Overview: Media file fundamentals

Media-file fundamentals distinguish the stored object, its encoded tracks and the terms used to describe its contents.

Before investigating playback, it helps to separate three questions: what kind of file is this, what does it carry, and how much data does it require? Container names, codec names and track descriptions answer different parts of that description. The topics here establish those distinctions, including the units behind bitrate and size and the meaning of lossy or lossless compression.

• What is a media file?
  A media file stores the data and instructions a player needs to reproduce recorded sound, pictures, or both.

• Containers and codecs
  A container organizes media streams, while codecs define how their picture and sound data are encoded.

• Streams and tracks
  A media track is a separately described sequence of video, audio, subtitles, or other data within a media source.

• Media file extensions
  A media file extension is a naming convention that hints at the file's format without proving its contents.

• Media MIME types
  A media MIME type labels the kind of content delivered by a protocol such as HTTP.

• Bitrate and file size
  Bitrate, duration and data units connect the amount of encoded media to its storage and delivery requirements.

• Lossy and lossless compression
  Lossless compression preserves the encoded input exactly, while lossy compression permits changes to reduce the amount of data.