THEO, Wowza & Fastly Present a Low-Latency HLS Solution

Since its release by Apple to combat scaling issues in 2009, HTTP Live Streaming (HLS), has become one of the most popular and widely supported streaming protocols today. Throughout the last decade we have seen the market change and the demand for lower latencies is higher than ever. In this Mini Guide we will discuss the most recent updates of Apple’s Low-Latency HLS (LL-HLS), and how THEO is working together with Fastly and Wowza to implement a seamless LL-HLS end-to-end solution.

THEO, Wowza & Fastly Present a Low-Latency HLS Solution (1)

Low-Latency HLS

From Twitter’s Periscope LHLS version in 2016, to the community’s L-HLS in 2018 and then LL-HLS from Apple in 2019, Low-Latency HLS is finally here. During the WWDC in June, Roger Pantos announced the spec is officially out of beta and LL-HLS will be available on iOS14, tvOS 14, watchOS 7, and macOS in Apple’s GA release (expected in October 2020). Further updates are also expected during Apple’s GA release.

The most important changes which make up LL-HLS include:

  • Blocking Playlist Updates: effectively reducing round trip times to retrieve an up to date playlist
  • Introduction of Parts: significantly reducing the delay between content creation and availability on the server
  • Preload Hints: further reducing delay between content creation and download ability by the client.
  • Delta Playlists: greatly reducing overhead introduced by frequent downloads of media playlists used to discover segments and parts.
  • Rendition Reports: allowing rapid retrieval of up-to-date playlists when switching variants.

Implementing an LL-HLS Solution

There have been many versions of Low-Latency HLS and vendors spearheading LL-HLS adoption have had to adapt with each revision, thus delaying development. The server and client must support the same version, not the older HTTP/2 PUSH-based version, or the intermediate draft version. While players and packaging vendors may have started implementation at different points in time, they might not cover all subtleties of the specification just yet. For example the latest version made blocking playlist reload optional instead of it being mandatory in the intermediate draft version. That said, the removal of HTTP/2 PUSH should simplify adoption, as this was initially a challenge for CDNs.

It’s crucial to have an end-to-end solution optimised for the latest version of the LL-HLS specification. Fastly Inc., THEO Technologies and Wowza Media Systems have worked closely together to give you a seamless end-to-end LL-HLS implementation, up-to-date with the latest version.

Overview of an LL-HLS end-to-end solution

Together, Fastly, THEO and Wowza have been testing to ensure full compatibility to allow customers to easily deploy Low-Latency HLS.

An End-to-End LL-HLS Solution with Fastly, THEO and Wowza
  1. An encoder will compress a stream using H.264/H.265 (HEVC)/... codecs for video and AAC/AC-3/… codecs for audio.
  2. From there, content is sent to the Wowza Streaming Engine server software for transcoding and packaging. Transcoding allows content distributors to generate adaptive bitrate renditions for delivery to users across varying bandwidth environments, whereas repackaging enables the creation of Low-Latency HLS video outputs. The media server is crucial to the conversion process required for streaming in LL-HLS for this reason. Specifically, it’s responsible for preparing the correct playlists with new tags, attributes, segments, and LL-HLS parts to be offered up to an origin.
  3. The origin also receives some additional responsibilities from an LL-HLS perspective. There are three major changes:
    • Where in the past, HLS did not require query parameters, the new HLS version allows for specific query parameters to be sent, which influence the presented playlist.
    • The origin also has to support blocking playlist reloads and blocking preload hints, meaning it has to be able to keep a request open for a longer time.
    • Finally, HTTP/2 is required to be supported on the origin.
  4. THEOplayer can request the relevant media information from Fastly’s global CDN, which in turn will request it from the origin - often via collapsing several requests using Fastly’s MediaShield. Fastly’s global CDN allows for global distribution and reduced latency, due to more cached content closer to the viewer.
  5. Finally, THEOplayer UVP remains responsible for refreshing the playlists, observing network capabilities and environments (and shifting to the correct variant stream when changes are detected), providing accessibility features such as subtitles and alternative audio tracks, etc.
Description of each company's LL-HLS solution

The underlying architecture of Fastly’s edge cloud platform is radically different from legacy CDNs. Utilizing a pull – rather than a push – model means our platform is format-agnostic. Fastly simply distributes the data, and you as the content owner maintain full control over the content delivery rather than waiting on a vendor to support new formats. This ensures efficient delivery and allows viewers to get the best possible experience. For example, Fastly was able to support HTTP3, QUIC, and Apple Low-Latency HLS as soon as the specs were released. The primary benefit of a format-agnostic approach is that it frees you from specific requirements normally imposed by your delivery chain, such as an encoder pushing specific formats or segment lengths. In other words, a pull model allows you to continuously experiment and optimize on your terms.

Fastly’s fully programmable developer’s edge, modern architecture and advanced request collapsing capabilities have allowed the edge cloud platform to become a leading innovator in live streaming and video delivery, accelerating customers’ time to success. As Fastly continues to push the envelope, this integration will serve as the foundation for advanced analytics, emerging low-latency technologies, and edge-compute capabilities that bring real-time processing and decision-making closer to the user.


THEOplayer UVP supports LL-HLS for content to play, including its new playlists, updates to support playlist parameters (delta playlist, sequence numbers, ...), a new download loop, executing blocking requests, as well as LL-HLS parts. To simplify, LL-HLS parts are the new segments where players should buffer three parts (with a relevant IDR-frame) and then playback can start. From there, THEOplayer UVP is responsible for everything it would do from a normal HLS perspective, meaning refreshing the playlists, observing network capabilities and environments (and shifting to the correct variant stream when changes are detected), providing accessibility features such as subtitles and alternative audio tracks, etc. THEO has optimized new ABR algorithms and bandwidth estimators in order to ensure an optimal experience while taking into account the specifics of LL-HLS (parts, preload-hints, ...).


Low-Latency HLS powered by Wowza enables broadcasters to stream content to a variety of endpoints with as low as two seconds in latency, while also ensuring backward compatibility with legacy clients. As one of the first vendors to implement support for the LL-HLS extension, Wowza’s video experts are committed to driving adoption of this emerging technology by developing against the evolving specification. Our LL-HLS solution integrates with CDNs and players to provide an end-to-end architecture for interactive streaming at scale, and we’re working to extend this functionality across our entire product portfolio.

Wowza’s live streaming platform plays an essential role in repackaging live content for LL-HLS streaming. Specifically, Wowza’s software generates partial segments using the fMP4 container format for low-latency delivery to the billions of active Apple devices (iPhone, iPad, iPod touch, and Apple TV) and desktop computers (macOS) around the world, as well as third-party platforms such as Android, Microsoft, and Linux.

Put simply, LL-HLS combines the simplicity, scalability, and quality of traditional HLS with significant improvements in latency. And by choosing Wowza, broadcasters can deploy these capabilities on-premises, hosted in the cloud, or as an SaaS solution.

Profile of each company

Fastly helps people stay better connected with the things they love. Expectations for online interactions are changing: consumers demand a fast, reliable, and secure internet experience. Fastly helps our customers exceed those expectations by creating great digital experiences quickly, securely, and reliably by processing, serving, and securing our customers’ applications as close to their end-users as possible, at the edge of the internet. This becomes more tangible with edge computing, which aims to move compute power and logic as close to the end-user as possible.


Founded in 2012, THEO is the go-to technology partner for media companies around the world. We aim to make streaming video better than broadcast by providing a portfolio of solutions, enabling for easy delivery of exceptional video experiences across any device or platform.

Our multi-award winning THEO Universal Video Player Solution, is trusted by hundreds of leading payTV and OTT service providers, broadcasters, and publishers worldwide. As the leader of Low Latency video delivery, THEO supports LL-HLS, LL-DASH and has invented High Efficiency Streaming Protocol (HESP) - allowing for sub-second latency streaming using low bandwidth with fast-zapping. Going the extra mile, we also work to standardise metadata delivery through the invention of Enriched Media Streaming Solution (EMSS).


Wowza is the global leader in live streaming solutions. Our full-service platform powers reliable, secure, low-latency video delivery for companies worldwide. With more than a decade of experience working with 35,000+ organizations in industries ranging from media and entertainment to healthcare and surveillance, Wowza provides the performance and flexibility that today’s businesses require. We work with each customer to ensure their success in putting streaming to work for their business. Our promise is simple: If you can dream it, Wowza can stream it.

Any questions left? Contact our THEO experts.

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