Is libaom Faster Than x265 for Video Encoding?
When comparing modern video codecs, encoding speed is a critical factor for developers and content creators deciding between AV1 and HEVC. This article provides a direct comparison of libaom (the reference encoder for AV1) and x265 (the industry-standard encoder for HEVC) regarding encoding time per frame. We will examine how architectural differences, optimization levels, and hardware utilization impact their performance, helping you determine which encoder fits your production workflow.
The Baseline: x265 Encoding Efficiency
The x265 encoder is highly mature and heavily optimized for modern CPU architectures, including AVX2 and AVX-512 instruction sets.
- Preset Scalability: x265 features a well-defined
spectrum of presets ranging from
ultrafasttoplacebo. - Frame Processing: In practical scenarios (like 1080p or 4K encoding), x265 can achieve near real-time or faster-than-real-time encoding on consumer-grade hardware using medium or fast presets. Its encoding time per frame is generally predictable and scales linearly with resolution and bitrate complexity.
The Contender: libaom Complexity
The libaom encoder was designed as a reference implementation for the AV1 format, prioritizing maximum compression efficiency over raw speed.
- Computation Heavy: AV1 utilizes much larger coding tree blocks (up to 128x128) and more complex intra/inter prediction modes than HEVC. This drastically increases the search space the encoder must process for every single frame.
- CPU Usage: Historically, libaom required orders of
magnitude more time per frame than x265. While recent updates (such as
libaom v3.x and beyond) have significantly improved threading and
introduced faster speed presets (
--cpu-used=6through9), it remains computationally heavier than x265.
Direct Comparison of Time Per Frame
To understand the actual gap in encoding time per frame, consider the following performance breakdown under typical encoding scenarios:
| Feature / Metric | x265 (HEVC) | libaom (AV1) |
|---|---|---|
| Average Time per Frame | Low to Medium (Milliseconds) | High to Very High (Seconds to Milliseconds) |
| Multi-threading Maturity | Excellent (Native frame/WPP threading) | Improving (Row-based/Tile threading required) |
| Real-time Capabilities | Highly capable at standard presets | Limited to high-speed presets with quality trade-offs |
| Compression-to-Speed Ratio | Balanced and production-ready | Superior compression, but at a steep time penalty |
At equivalent quality targets, libaom can take anywhere from 2x to 5x longer per frame than x265, even when utilizing libaom’s newer speed-optimized settings. For archival or highest-quality settings, libaom’s encoding time per frame can skyrocket, making it less viable for time-sensitive or live-streaming deployments without specialized hardware acceleration.