What is an Encoding Ladder?
An encoding ladder refers to the various configurations used for delivering both Video-On-Demand and live content to different devices with varying connection speeds across a range of data rates and resolutions. An encoding Ladder is a set of options for optimizing video content delivery across different platforms and devices.
The first significant encoding ladder was developed and introduced by Apple in Tech Note TN2224. This was a significant milestone in the field of video content delivery, as it allowed content providers to tailor their delivery strategies to the specific needs of their audiences. Since then, the encoding ladder has become an essential tool for content providers across the industry.
How Encoding Ladders Work
The main function of an encoding ladder is to ensure that video content can be delivered to devices with varying specifications by making it available at different quality levels. Using an encoding ladder, all VODs or live videos intended for streaming are encoded into several streams, each with varying quality.
Apple's encoding ladder offers robust video encoding capabilities, providing at least ten different streams to choose from. Many producers and video creators use this ladder to deliver their services with little to no modifications or with minor configuration tweaks.
How To Create an Encoding Ladder?
In simple terms, creating an encoding ladder involves four major steps:
- Determining the floor: This is the lowest bitrate your encoding ladder will support.
- Determining the ceiling: This is the highest bitrate your encoding ladder will support.
- Determining intermediate bitrates: You must choose the bitrates for the rungs between the ceiling and the floor.
- Determining resolutions for different rungs: To optimize video delivery, you need to choose appropriate resolutions for each rung.
Correlation Between Encoding Ladders and Codecs
Video codecs have a close relationship with encoding ladders. Whether you opt for a per-title or static approach, you need to select encoding ladders based on the codec you're using to deliver the video.
For example, Apple recommends using two separate ladders for the H.264 and HEVC codecs, while VP9 and AV1 codecs require different ladders. This requirement is logical because codecs tend to become more efficient over time, meaning that newer codecs can provide lower bitrates at higher resolutions.