What is HLS? An in-depth look at the streaming protocol and the SPCast solution

HLS (HTTP Live Streaming) is a streaming protocol developed by Apple that has revolutionized the transmission of audio and video files over the internet. Today, it is the means of choice for live events and on-demand streaming on a variety of end devices such as computers, smartphones, tablets and smart TVs.

An often underestimated point: Although HLS is often associated with video, it works excellently for pure audio content and offers a stability that classic protocols often do not achieve.

How does HLS work in detail?

The main mechanism of HLS is not to send the data stream as one uninterrupted “block”, but to divide it into small segments. These segments are transmitted to the client via the standard HTTP protocol.

  • Segmentation: Each segment has a fixed duration, typically between 2 and 10 seconds.
  • The playlist file (M3U8): When a user opens an HLS URL, the client first loads the so-called M3U8 file. This acts as an index and contains the URLs of the individual segment files as well as information about available bit rates.
  • Playback: The client selects the appropriate stream, downloads the segments one after the other and puts them together seamlessly for the listener.

Advantages of HLS compared to other protocols

HLS offers significant advantages that have made it the industry standard.

  • Adaptive Streaming (ABR): HLS dynamically adapts the quality of the stream to the network conditions. If the internet connection fluctuates, the player automatically reduces the bit rate to avoid buffer pauses.
  • Compatibility: HLS is natively supported by all Apple devices and Android. On desktop browsers (Chrome, Firefox, Edge), playback is now possible across the board thanks to modern web technologies (MSE).
  • Scalability: As HLS is based on HTTP, content can be distributed efficiently via content delivery networks (CDNs). This makes it possible to serve a massive number of simultaneous listeners without overloading the origin server.
  • Reusability: Segmentation enables simple storage and archiving so that users can easily retrieve content at different times.

HLS in SPCast: The technical challenge

You have to understand: HLS is very “rigid” by nature. The protocol is not actually intended for dynamic changes of sources or mount points within a running stream. In the standard implementation, a change of signal source necessarily causes the listener to drop out or the HLS stream to stop.

Note for use in SPCast before version 0.9.9.097

In older versions, HLS should be used with caution due to this protocol-related rigidity:

  • No fallback functions: Automatic fallback solutions are not available.
  • Mountpoint switching issues: Seamless transition between AutoDJ and live source does not work when broadcasting via SPCast moderator accounts.
  • Restricted transitions: The transitions only work if you send directly via the AutoDJ, as the mount point is not changed here.
  • Recommendation: Do not use HLS references here as a standard for directories, but rather point users specifically to their use.

The solution: HLS in SPCast from version 0.9.9.097

Since: 16.02.2026

Since version 0.9.9.097, HLS is no longer subject to any restrictions in SPCast systems. All the problems of older versions described above are obsolete.

Since the HLS protocol itself is not designed for such flexibility, we have developed our own solution that works “around the protocol”. This development makes it possible to map the three critical conditions (live change, mountpoint change, fallbacks) seamlessly and stably, which would not normally be possible with native HLS.