What is the difference between good and realtime deadline modes in libaom?

When encoding video using the AV1 codec via libaom, choosing the right deadline mode is critical for balancing processing speed and visual quality. This article breaks down the fundamental differences between the good and realtime deadline settings, explaining how they manage compression algorithms, their primary use cases, and how to choose the best option for your video project.

The Purpose of Deadline Modes in Libaom

In libaom, the --deadline (or -usage in newer versions) parameter tells the encoder how much time it is allowed to spend compressing each frame. Because AV1 is an incredibly complex codec, these modes act as high-level profiles that dictate whether the encoder should prioritize maximum compression efficiency or raw processing speed.

Good Quality Mode (`--deadline=good`)

The good mode is the default setting for libaom and is designed for file-based, ahead-of-time encoding.

How it works: It enables exhaustive searching of coding tools, deep motion estimation, and advanced psychoacoustic optimizations. The encoder takes as much time as necessary (within your specified CPU-used preset) to deliver the highest possible visual quality at the lowest possible bitrate.
Best Used For: Video-on-demand (VOD) streaming, archiving movies, creating high-quality web assets, or any scenario where encoding time is not a constraint.

Realtime Mode (`--deadline=realtime`)

The realtime mode is specifically engineered for low-latency, live video scenarios.

How it works: It bypasses the most computationally expensive AV1 encoding tools and enforces strict time constraints on frame processing. The encoder compromises on compression efficiency—meaning you will need a higher bitrate to match the visual quality of good mode—in order to guarantee that frames are encoded fast enough to prevent buffering during a live stream.
Best Used For: Live streaming, video conferencing (e.g., WebRTC applications), cloud gaming, and real-time broadcasting.

Key Differences at a Glance

Feature	Good Mode (`good`)	Realtime Mode (`realtime`)
Primary Focus	Maximum visual quality and compression efficiency.	Ultra-low latency and fast encoding speed.
Encoding Speed	Slow to very slow.	Extremely fast, capable of 30+ FPS live encoding.
Bitrate Efficiency	High (smaller file sizes for the same quality).	Lower (requires higher bitrates to avoid artifacts).
Algorithmic Depth	Uses deep motion vector searches and complex block partitioning.	Disables heavy tools; utilizes fast motion estimation and speed-optimized heuristics.

Which Mode Should You Choose?

Choose Good Mode if your video is pre-recorded. If you are uploading a video to YouTube, archiving a family video, or mastering a film, you want the best quality per gigabyte, making good the correct choice.
Choose Realtime Mode if your video is interactive or live. If you are building a video chat app or streaming live gameplay where frames must be encoded and transmitted instantly, realtime is required to avoid breaking the live experience.