How to Build an Encoding Ladder: What You Need to Know

Jan Ozer February 11, 2023 Articles, Codecs, Encoding, FFmpeg Leave a comment 927 Views

Learning how to build an encoding ladder is one of the most fundamental tasks for a streaming media professional. It’s astounding how much you need to know to get it right.

By way of background, the original encoding ladder used by most professionals was from Apple Tech Note TN2224, long since replaced by Apple’s HLS Authoring Specifications. This H.264-only ladder had defined rungs, resolutions, and bitrates, and was the starting point for a startling array of encoding ladders used around the web. I’ve always loved Beamr’s image that showed TN2224 at the center of the Rosetta Stone for working with encoding ladders.

Apple TN2224 was the Rosetta Stone for learning how to build an encoding ladder. — The original encoding ladder from Apple’s Tech Note TN2224 was the Rosetta Stone for learning how to build an encoding ladder (image courtesy of Beamr).

Since Apple replaced TN2224 back in 2017, learning how to build an encoding ladder has gotten much more complicated, and the discrete bits of knowledge you need to know to get it right have ballooned. Here’s an example; a simple five-rung HEVC live encoding bitrate ladder produced in FFmpeg.

ffmpeg -y -re -i input.mp4 \ -c:v libx265 -preset ultrafast -x265-params keyint=60:min-keyint=60:scenecut=0:bitrate=6000:vbv-maxrate=6000:vbv-buf-size=6000:open-gop=1 out_1080p_6MB_x265.mp4 \ -c:v libx265 -preset ultrafast -x265-params keyint=60:min-keyint=60:scenecut=0:bitrate=4000:vbv-maxrate=4000:vbv-buf-size=4000:open-gop=1 out_1080p_4MB_x265.mp4 \ -c:v libx265 -s 1280x720 -preset ultrafast -x265-params keyint=60:min-keyint=60:scenecut=0:bitrate=2500:vbv-maxrate=2500:vbv-buf-size=2500:open-gop=1 out_720p_2_5MB_x265.mp4 \ -c:v libx265 -s 960x540 -preset ultrafast -x265-params keyint=60:min-keyint=60:scenecut=0:bitrate=1200:vbv-maxrate=1200:vbv-buf-size=1200:open-gop=1 out_540p_1_2MB_x265.mp4 \ -c:v libx265 -s 640x360 -preset ultrafast -x265-params keyint=60:min-keyint=60:scenecut=0:bitrate=800:vbv-maxrate=800:vbv-buf-size=800:open-gop=1 out_360p_800kb_x265.mp4

Below are links to pages discussing all the topics you need to know to get right. Explicit choices are decisions shown in the encoding ladder. Implicit choices are choices made by default in the encoding ladder. Other choices not discussed are issues worth being aware of that may not be reflected in the encoding ladder.

I review the decisions individually on separate pages; pages without links mean the page isn’t complete. Most of these are links to articles I’ve written; over time, I’ll convert them to more concise articles for each subject.

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