What are HLS tags?

HTTP Live Streaming (HLS) tags are part of the protocol developed by Apple for use in their streaming services. They appear in HLS playlist files (also known as manifest files) to specify streaming metadata for a particular stream. These files have an .m3u8 extension and contain a sequence of tags and URIs.

The tags provide important instructions or metadata for the stream. Here are some examples:

#EXTM3U: This is the file header and should be the first line of every .m3u8 file.
#EXT-X-VERSION: This specifies the compatibility version of the playlist file.
#EXT-X-TARGETDURATION: This specifies the maximum duration of any media segment in the playlist.
#EXT-X-MEDIA-SEQUENCE: This specifies the sequence number of the first segment in the playlist.
#EXT-X-STREAM-INF: This is used in master playlists to give details about a variant stream, including bandwidth, resolution, and codecs.
#EXT-X-ENDLIST: This indicates that no more media segments will be added to the playlist.

And many others. The exact usage and requirement of these tags can be found in the HLS specification documentation. Please note that the implementation of new tags and deprecation of old ones may occur over time as the protocol evolves.

Article written by
Sylvain Corvaisier

Independent streaming and iOS engineer

Last modified: January 13th, 2025