Moov

Moov is the name commonly used for the Movie Box, a container atom in the ISO base media file format used by MP4 and QuickTime files. The moov atom holds file-wide metadata that describes how the media tracks are organized and how they should be played.

Within moov there are nested boxes such as mvhd (movie header) containing timescale and duration; trak boxes for each track; within each trak is mdia, which contains mdhd (media header), hdlr (handler), and minf (media information). The sample table stbl provides stsd, stts, stsc, stsz, and stco or co64 entries that map samples to time and file offsets. There may also be udta (user data) and meta boxes.

Role in playback: The moov box provides essential indexing and timing information needed to decode and display video and audio. Without a readable moov, most players cannot seek or present the media correctly.

Positioning: In the typical streaming-friendly layout, the moov box is placed before the mdat box, so a player can start playback without downloading the entire file; some encoders repackage files to move moov to the front (a process known as faststart).