CMAF
CMAF (Common Media Application Format) is a streaming standard that defines one shared fragmented MP4 format for video segments used by both HLS and MPEG-DASH. Before CMAF, services often stored the same video twice, once in TS for HLS and once in MP4 for DASH. CMAF also supports chunked delivery, which helps cut live streaming latency.
Why it matters
Before CMAF, many services encoded and stored every title twice, once for HLS and once for DASH. CMAF lets one set of segments serve both, which lowers storage, CDN and encoding costs. Its chunked mode also helps live streams reach viewers with less delay.
How it works
- Video is encoded once at several quality levels.
- Each quality level is packaged into fragmented MP4 segments following CMAF rules.
- An HLS playlist and a DASH manifest both point to the same segment files.
- For low latency, segments are split into smaller chunks that are sent as soon as each is ready.
Is CMAF the same as HLS or DASH?
No, CMAF is not a streaming protocol like HLS or DASH. It is a shared media format that both protocols can use. HLS and DASH still use their own manifests, M3U8 and MPD, but with CMAF those manifests can point to the same fragmented MP4 segments.
Does CMAF reduce latency?
CMAF can reduce latency when chunked encoding and transfer are used, but the format alone does not. Chunks let a player receive part of a segment before the whole segment is finished. Combined with low-latency HLS or low-latency DASH, delays of a few seconds are achievable.
Does CMAF work with DRM?
Yes, CMAF works with DRM through common encryption (CENC). One encrypted set of segments can be unlocked by different DRM systems, such as Widevine, PlayReady and FairPlay. Different devices still need compatible encryption modes, so many services use the cbcs mode for broad support. On-demand DRM is priced at $99/month plus a fee per license.
Where it's used
OTT services and video platforms use CMAF to keep one set of video files for Apple and non-Apple devices, cutting storage. Live sports streamers also use its chunked mode to reduce delay.
By the numbers
- CMAF was first published as the ISO/IEC standard 23000-19 in January 2018 and has since been revised. (ISO/IEC 23000-19:2018 (ISO))
