December 01, 2014 by Romain Bouqueau

Apple HLS: comparing versions

An introduction to Apple HLS is available as: Apple HLS: introduction. A technical analysis of the versions is available as: Apple HLS: technical in-depth.

Versions and revisions

HLS comes in different versions. As of when this article is written, version numbers range from 1 to 10. Version 3 and 7 are the most popular. You'll learn why by reading the table below.

Each of the version is covered by one or more revisions. The HLS draft revisions covered in this analysis range from 0 to 23 for RFC8216. Draft revision 23 is the IETF RFC8216 since August 31, 2017.

Then Apple started publishing updates in the IETF RFC8216-bis draft. Current revision numbers range from 0 (same as RFC8216) to 10.

Outdated note: if you look closely at the dates in the table, you'll notice that revisions are generally not separated by more than 6 months from the previous. That's because the HLS specification has been available as an IETF draft. IETF drafts automatically expire after 6 months. Thanks to Nicolas Weil for the reminder. Therefore Apple HLS has been available as a draft since May 1, 2009 i.e. for more than five years. We have no information of Apple planning to finalize it. PS: RFC finalized in 2017, see below.

You can find the correspondence between 'version' and 'revision' in the table below. You can find the correspondence between revisions and iOS versions in this Apple developer page (thanks to G. Du Pontavice from flashls):

revision	version	date	new features
0	1	May 1, 2009	Initial release
1	1	June 8, 2009
2	1	October 5, 2009
3	2	April 2, 2010	Specifying the resolution for video variant streams. Improving encryption (initialization vector). Introducing version compatibility.
4	2	June 5, 2010
5	3	November 19, 2010	Introducing the playlist-type (VOD, Event)
6	3	March 31, 2011
7	4	September 30, 2011	Audio and Video can be specified separately (e.g. unmuxed together), introducing rendition groups. Introducing byte-ranges to access the content from a single file. Allowing special playlists containing only I-frames (i.e. access points).
8	4	March 23, 2012
9	5	September 22, 2012	Subtitles (WebVTT). Adding a new per-sample encryption scheme.
10	5	October 15, 2012
11	5	April 16, 2013
12	6	October 14, 2013	Introduce Closed-Captions (in addition to subtitles). Error resilience: discontinuity and independence of each segment can be signalled in the playlist.
13	6	April 16, 2014
14	7	October 14, 2014	Adding alternate renditions signalling. Adding session data. Closed-Captions: support for CEA-708.
15	7	April 15, 2015	AC-3 and eAC-3. FRAME-RATE attribute in EXT-X-STREAM-INF.
16	7	April 15, 2015	Bitrate definition clarified: it doesn't include network (HTTP, TCP, IP) overhead. Multiple EXT-X-VERSION are now rejected. TYPE attribute of EXT-X-MEDIA is now mandatory. Removed FRAME-RATE attribute introduced in revision 16 (the same day ;) ).
17	7	October 16, 2015	Use of MUST and SHOULD keywords as in RFC2119.
18	7	November 19, 2015
19	7	April 4, 2016	Adding EXT-X-DATERANGE (with SCTE35 specific attributes)
20	7	September 20, 2016	Adding MPEG-4 Fragmented as a container. explicit use of MP3 and (Enhanced) AC-3 audio codecs.
21	7	March 27, 2017
22	7	April 24, 2017
23	7	May 22, 2017	Mentions to CMAF for MPEG-4 Fragmented.
RFC8216	7	August 31, 2017	Same as draft revision 23.
RFC8216bis	8	December 8, 2017	Version 8. No major new feature.
RFC8216bis	10	April 8, 2020 (last updated on 8 November 2022)	Note: there was no version 9. LL-HLS: low latency. Content Steering. Explicit interstitial content.

The latest version of the Apple HLS IETF document can be found here.