Fragmented MP4 (fMP4)
Fragmented MP4 (fMP4) is a version of the MP4 format that splits video into small, self-contained fragments instead of one continuous file. Each fragment holds a few seconds of media and its own timing information. This makes fMP4 well suited to adaptive streaming, because players can request and play pieces without downloading the whole file.
Why it matters
fMP4 lets one set of encoded files serve both HLS and DASH players, which cuts storage and encoding costs. It is also required for newer codecs on Apple devices and supports common encryption for DRM. Choosing fMP4 keeps a streaming setup ready for HEVC, AV1 and low latency.
How it works
- An initialization segment holds setup data, such as codec details, that the player reads once.
- The video is split into fragments, each with a moof box (timing index) and an mdat box (media).
- Each fragment is saved as its own segment file or as a byte range in one file.
- The player reads the manifest, loads the init segment, then downloads fragments in order.
What is the difference between MP4 and fragmented MP4?
A regular MP4 keeps one index for the whole file, while fragmented MP4 gives each short piece its own index. That means an fMP4 player can start from any fragment without the full file. Regular MP4 suits downloads; fMP4 suits adaptive and live streaming.
Does HLS support fMP4?
Yes, HLS supports fMP4 segments alongside the older MPEG-TS segments. Apple requires fMP4 for HEVC and AV1 video in HLS. Using fMP4 also lets the same segments be reused for MPEG-DASH through CMAF, so you store one copy instead of two.
Is fMP4 better than TS?
For most new streaming setups, yes, fMP4 is the better choice. It has less overhead, supports newer codecs and common encryption, and works with both HLS and DASH. TS remains useful for very old players and broadcast workflows that already depend on it.
Where it's used
OTT services, creator apps and video platforms store videos as fMP4 segments so one encoded copy can serve both Apple and Android players, including DRM-protected content.
By the numbers
- Apple's HLS authoring rules require fragmented MP4 as the container for HEVC and for AV1 video. (HLS Authoring Specification for Apple Devices)
