Adaptative streaming basics

✔️ The media player is provided with different renditions of the video to play.

✔️ Media renditions can vary in display size (resolution) and file size (bitrate)

✔️ HLS (HTTP Live Streaming) is the standard protocol for adaptative streaming :

• It allows media players to pick the best media rendition for the available bandwidth at any given moment, thus avoiding buffering during playback
• Media renditions are produced by :
  1. Transcoding the original media to the requested bitrate and resolution and split the result into 2-12 seconds segments (*.ts)
  2. Creating a rendition manifest (*.m3u8) that contains the paths to the segments
• Finally a master manifest (*.m3u8) is created, that contains informations about the available renditions manifests

✔️ DASH (Dynamic Adaptive Streaming over HTTP) is another protocol for adaptative bitrate streaming that uses XML files instead of plaintext files

✔️ MP4 and WebM do not support adaptative streaming, meaning that they will always buffer when the available bandwitdth diminishes

✔️ Adaptative bitrate streaming enables vertical scaling of content delivery by providing the best possible experience for the available bandwidth

✔️ CDNs (content delivery networks) enable horizontal scaling of content delivery by :

• Relying on a geographically distributed networks of content servers
• Caching the requested content from the origin server after it is first requested
• Allowing all subsequent requests for the same content to be delivered from a location physically close to the viewer

✔️ Different CDNs can best accomodate delivery needs for a multitude of different users, it is thus a common strategy to use multiple CDNs as a global distributed content cache when reaching out for a large audience

✔️ The goal is to achieve low latency when streaming over HTTP using HLS or DASH