librav1e Architecture Roadmap and Future Changes

This article outlines the planned architectural roadmap and future technical changes for librav1e, the library interface of the Rust-written AV1 video encoder, rav1e. It covers the strategic shift toward advanced threading models, deeper SIMD assembly integration, memory allocation optimizations, and enhancements to the C-compatible API for seamless integration into external multimedia frameworks.

Multi-Threading and Parallelism Redesign

The primary architectural focus for future versions of librav1e is the overhaul of its threading model. While current iterations support basic tile-based and frame-based parallelism, future updates aim to implement fine-grained row-level (wavefront) parallel processing.

This change will allow the encoder to distribute the workload of a single frame across multiple CPU cores more efficiently, significantly reducing latency and improving hardware utilization on high-core-count systems. The scheduler is being refactored to minimize synchronization overhead between threads, ensuring that dependencies between blocks are resolved with minimal idle CPU time.

Deeper SIMD and Assembly Integration

To compete with mature C-based encoders, librav1e is restructuring how Rust code interacts with assembly optimizations. The roadmap highlights a push for deeper integration of hand-written assembly for performance-critical pipelines:

• AVX2 and AVX-512: Further offloading of transform, quantization, and motion estimation loops to AVX-512 instruction sets.
• ARM Neon: Improving performance on mobile and Apple Silicon architectures by expanding Neon assembly coverage.
• Rust-Assembly Boundary Optimization: Minimizing the overhead of calling external assembly functions from Rust by grouping operations and reducing context-switching within the hot loops of the encoder.

Memory Footprint and Allocation Reductions

Reducing memory usage and improving cache locality is another major milestone. The upcoming architectural changes include a transition to a more static memory allocation model. Instead of allocating memory dynamically during the encoding of a frame, librav1e will move toward pre-allocating reusable buffers at the start of the encoding session. This change will eliminate memory fragmentation, reduce garbage collection-like overhead in long-running encoding passes, and ensure predictable performance in resource-constrained environments.

API Stabilization and C-Bindings (librav1e)

As the underlying Rust engine matures, the C-compatible interface (librav1e) is undergoing refinement to make it a first-class citizen for downstream projects like FFmpeg, GStreamer, and HandBrake. The roadmap details the following API enhancements:

• Opaque Data Structures: Transitioning internal states to fully opaque structures to allow internal architectural changes without breaking binary compatibility (ABI).
• Granular Rate Control API: Exposing deeper rate-control hooks to external applications, enabling two-pass encoding configurations to be handled more precisely by host applications.
• Improved Error Handling: Translating internal Rust panics and complex error states into standard, predictable C error codes to prevent host application crashes.

Perceptual Quality and Rate Control Refinement

Beyond raw performance, the architectural pipeline is being adjusted to better support psychoacoustic and perceptual video coding. Future updates will introduce a modular framework for scene change detection and variance-guided quantization. This modularity will allow developers to plug in custom tuning metrics (such as butteraugli or SSIMULACRA2) directly into the encoding pipeline, allowing librav1e to dynamically allocate bits to areas of a frame that are most noticeable to the human eye.