rav1d-safe

A safe Rust AV1 decoder. Forked from rav1d, with 160k lines of hand-written x86/ARM assembly replaced by safe Rust SIMD intrinsics.

578 commits since the fork (+90,813 / -6,958 lines across 1,194 files). 68k of those net new lines are safe SIMD in src/safe_simd/.

Quick Start

Add to your Cargo.toml:

[dependencies]
rav1d-safe = "0.5"

Decode an AV1 bitstream:

use rav1d_safe::{Decoder, Planes};

fn decode(obu_data: &[u8]) -> Result<(), Box<dyn std::error::Error>> {
    let mut decoder = Decoder::new()?;

    // Feed raw OBU data (not IVF/WebM containers)
    if let Some(frame) = decoder.decode(obu_data)? {
        println!("{}x{} @ {}bpc", frame.width(), frame.height(), frame.bit_depth());

        match frame.planes() {
            Planes::Depth8(planes) => {
                for row in planes.y().rows() {
                    // row is &[u8] — zero-copy, no allocation
                }
            }
            Planes::Depth16(planes) => {
                let px = planes.y().pixel(0, 0); // 10 or 12-bit value
            }
        }
    }

    // Drain any buffered frames
    for frame in decoder.flush()? {
        // ...
    }
    Ok(())
}

API Overview

The public API lives in src/managed.rs and is re-exported at the crate root.

Core types:

Type	Purpose
Decoder	Decodes AV1 OBU data into frames
Frame	Decoded frame with metadata (cloneable, Arc-backed)
Planes	Enum dispatching to Planes8 or Planes16 by bit depth
PlaneView8 / PlaneView16	Zero-copy 2D view with row(), pixel(), rows()
Settings	Thread count, film grain, filters, frame size limit, CPU level
CpuLevel	SIMD dispatch level (Scalar, X86V2, X86V3, X86V4, Neon, Native)
Error	Enum: InvalidData, OutOfMemory, NeedMoreData, etc.

Metadata types: ColorInfo, ColorPrimaries, TransferCharacteristics, MatrixCoefficients, ColorRange, ContentLightLevel, MasteringDisplay, PixelLayout

Input Format

The decoder expects raw AV1 Open Bitstream Unit (OBU) data. If you have IVF or WebM containers, strip the container framing first and pass the OBU payload. See tests/ivf_parser.rs for an IVF parser example. For AVIF images, use zenavif-parse to extract the OBU data from the ISOBMFF container.

Threading

use rav1d_safe::{Decoder, Settings, CpuLevel};

// Single-threaded (default) — synchronous, deterministic
let decoder = Decoder::new()?;

// Multi-threaded — frame threading, better throughput
let decoder = Decoder::with_settings(Settings {
    threads: 0, // auto-detect core count
    ..Default::default()
})?;

// Constrained decoding — limit frame size and CPU features
let decoder = Decoder::with_settings(Settings {
    frame_size_limit: 3840 * 2160, // reject frames larger than 4K
    cpu_level: CpuLevel::Native,   // use best available SIMD
    ..Default::default()
})?;

With threads >= 2 or threads == 0, the decoder uses tile threading to parallelize decode within each frame. decode() may return None for complete frames because processing is asynchronous — call it repeatedly or use flush() to drain.

Tile threading works under forbid(unsafe_code) without the unchecked feature. No special feature flags needed:

rav1d-safe = { version = "0.5", features = ["bitdepth_8", "bitdepth_16"] }

With 2 threads, expect ~2x speedup on photo decode. Frame threading (max_frame_delay > 1) still requires the unchecked feature.

HDR Metadata

if let Some(cll) = frame.content_light() {
    println!("MaxCLL: {} nits", cll.max_content_light_level);
}
if let Some(mdcv) = frame.mastering_display() {
    println!("Peak: {} nits", mdcv.max_luminance_nits());
}
let color = frame.color_info();
// color.primaries, color.transfer_characteristics, color.matrix_coefficients

Error Handling

All fallible operations return Result<T, rav1d_safe::Error>. Error variants: InvalidData, OutOfMemory, NeedMoreData, InitFailed, InvalidSettings, Other.

Safety Model

The default build (forbid(unsafe_code) crate-wide) contains zero unsafe in the main crate. The only unsafe code lives in the rav1d-disjoint-mut workspace sub-crate, a provably sound RefCell-for-ranges abstraction with always-on bounds checking.

The SIMD path uses:

• archmage for token-based target-feature dispatch (no manual #[target_feature])
• safe_unaligned_simd for reference-based SIMD load/store (no raw pointers)
• Value-type SIMD intrinsics, which are safe functions since Rust 1.93
• Slice-based APIs throughout — no pointer arithmetic in SIMD code

Verify at runtime with rav1d_safe::enabled_features() — returns a comma-delimited list including the active safety level (e.g. "bitdepth_8, bitdepth_16, safety:forbid-unsafe").

What's Been Ported

The default build compiles under forbid(unsafe_code) in the main crate. All SIMD work lives in src/safe_simd/ (59k lines of safe Rust replacing 233k lines of hand-written assembly across x86 and ARM).

Ported: All DSP Kernels (AVX2 + NEON)

Every DSP kernel family has a safe Rust SIMD implementation that compiles under forbid(unsafe_code):

Module	x86 ASM replaced	ARM ASM replaced	Safe Rust
mc (motion compensation)	3 files (SSE/AVX2/AVX-512) x2 bitdepths	4 files (32+64-bit) x2 bitdepths + SVE/dotprod	mc.rs + mc_arm.rs
itx (inverse transforms)	3 files x2 bitdepths	2 files x2 bitdepths	itx.rs + itx_arm.rs
ipred (intra prediction)	3 files x2 bitdepths	2 files x2 bitdepths	ipred.rs + ipred_arm.rs
cdef (directional enhancement)	3 files x2 bitdepths	2+tmpl files x2 bitdepths	cdef.rs + cdef_arm.rs
loopfilter	3 files x2 bitdepths	2 files x2 bitdepths	loopfilter.rs + loopfilter_arm.rs
looprestoration (Wiener + SGR)	3 files x2 bitdepths	2+common+tmpl files x2 bitdepths	looprestoration.rs + looprestoration_arm.rs
filmgrain	3+common files x2 bitdepths	2 files x2 bitdepths	filmgrain.rs + filmgrain_arm.rs
pal (palette)	1 file	(none — ARM uses scalar)	pal.rs
refmvs (reference MVs)	1 file	2 files (32+64-bit)	refmvs.rs + refmvs_arm.rs
msac (entropy decoder)	1 file (shared)	1 file (shared)	inline in msac.rs
cpuid	1 file (55 lines)	—	replaced by std::arch detection in cpu.rs

msac uses branchless scalar for adapt4/adapt8 and a serial loop with early exit for adapt16. When the unchecked feature is enabled on x86_64, adapt4/adapt8/hi_tok switch to inlined SSE2 intrinsics via the sse2!() macro pattern (no function call overhead). The bool functions (bool_adapt, bool_equi) stay scalar — they have no data parallelism to exploit.

Not Ported (With Rationale)

Scaled MC (put_8tap_scaled, prep_8tap_scaled, put_bilin_scaled, prep_bilin_scaled) — These functions use per-pixel variable step sizes with per-pixel filter selection, making them fundamentally different from fixed-block MC. The ASM versions are heavily register-scheduled for this pattern. Falls back to scalar Rust. ~2% of profile on inter-frame content.

SSE-only paths — 14 files, ~52k lines. The safe SIMD dispatch jumps straight to AVX2 when available. On pre-AVX2 hardware (pre-Haswell, 2013), the decoder falls back to scalar Rust rather than SSE intrinsics. SSE-only x86 hardware is rare enough that maintaining a second intrinsics tier isn't worth the code.

ARM SVE2, dotprod, i8mm extensions — mc_dotprod.S (1,880 lines) and mc16_sve.S (1,649 lines) are optional fast paths for newer ARM cores. The safe SIMD covers baseline NEON; these extension paths fall back to the NEON implementation.

Remaining AVX-512 paths — Some AVX-512 paths have been ported (itx, mc, ipred, looprestoration Wiener), but others remain unported. Falls back to AVX2 where not implemented.

ASM infrastructure files — x86inc.asm (1,983 lines), asm.S, util.S, *_tmpl.S, *_common.S are macro libraries and constants that only exist to support the raw assembly. No independent functionality to port.

Performance

All benchmarks: x86_64 (Zen 4, AVX2), single-threaded, Rust 1.93+, fat LTO. Run with just profile (500 iterations for IVF, 20 iterations for AVIF).

Real photographs (AVIF decode, single image)

Single still images at web-typical quality (YUV420, q60). Source: Google-native 8K photo, downscaled with ImageMagick. These numbers reflect real-world AVIF decode performance where SIMD kernels dominate.

Resolution	ASM	Safe (checked)	Safe (unchecked)	Safe vs ASM
4K (3840x2561)	122 ms	246 ms	234 ms	2.0x
8K (8192x5464)	724 ms	1319 ms	1289 ms	1.8x

Small test vectors (IVF, multi-frame decode)

dav1d-test-data allintra 352x288 (39 frames). Entropy-heavy bitstream where the serial msac decoder dominates, which compresses the ratio compared to pixel-heavy workloads.

Build	ms/iter	ms/frame	vs ASM
ASM	107.3	2.75	1.0x
Safe (checked)	173.1	4.44	1.61x
Safe (unchecked)	164.1	4.21	1.53x

Where the gap comes from

The safe build is ~2x slower on real images and ~1.7x on entropy-heavy vectors. The gap breaks down:

• Entropy decoder (msac): ~35% of decode time. Serial dependency chain — the core symbol decode loop can't be parallelized. The partial_asm feature uses hand-tuned ASM for msac and loopfilter, bringing real photo decodes down to 1.4-1.5x vs full ASM.
• Calling conventions: The ASM kernels use custom register allocation across function boundaries. Rust's ABI reloads registers at each call site.
• Scaled MC: Falls back to scalar Rust (~2% of inter-frame content). The ASM version uses per-pixel variable-step register scheduling that doesn't map cleanly to safe intrinsics.
• Bounds checking: The unchecked feature skips DisjointMut borrow tracking. This saves ~5% on photos, confirming the tracking overhead is modest.

Reproduce locally

just generate-bench-avif  # create 4K/8K AVIF test images (requires avifdec + avifenc)
just profile              # all four modes side-by-side (ASM, partial ASM, checked, unchecked)
just profile-quick        # same with fewer iterations

Conformance

Tested against the dav1d-test-data suite. MD5 hashes verified at all CPU dispatch levels (scalar, SSE4.2, AVX2, native).

784 of 803 test vectors pass across all levels.

19 vectors are not exercised by the test harness:

Category	Count	Reason
sframe	1	Requires S-frame support
svc (operating points)	6	Always decodes at default operating point
argon (vq_suite)	12	Various decode modes and operating point selection tests

Run conformance tests with cargo test --release --test decode_cpu_levels.

Building

Requires Rust 1.93+ (stable). Install via rustup.rs.

# Default safe-SIMD build (recommended)
cargo build --release

# With original hand-written assembly (for benchmarking)
cargo build --features asm --release

# Run tests
cargo test --release

Feature Flags

Feature	Default	Description
bitdepth_8	on	8-bit pixel support
bitdepth_16	on	10/12-bit pixel support
unchecked	off	Skip DisjointMut borrow tracking; enables frame threading and SSE2 msac on x86_64
partial_asm	off	ASM for entropy decoding (msac) and loopfilter only; safe SIMD everything else. Implies unchecked
c-ffi	off	C API entry points (dav1d_* symbols). Implies unchecked
asm	off	Full hand-written assembly. Implies c-ffi

Safety chain: default (forbid(unsafe_code), tile threading) -> unchecked (frame threading) -> c-ffi -> asm. Each level relaxes the safety constraint.

Cross-Compilation

# aarch64
RUSTFLAGS="-C linker=aarch64-linux-gnu-gcc" \
  cargo build --target aarch64-unknown-linux-gnu --release

# Verify aarch64 NEON compiles
cargo check --target aarch64-unknown-linux-gnu

Supported targets: x86_64-unknown-linux-gnu, aarch64-unknown-linux-gnu, i686-unknown-linux-gnu, armv7-unknown-linux-gnueabihf, riscv64gc-unknown-linux-gnu.

Image tech I maintain

State of the art codecs*	zenjpeg · zenpng · zenwebp · zengif · zenavif (rav1d-safe · zenrav1e · zenavif-parse · zenavif-serialize) · zenjxl (jxl-encoder · zenjxl-decoder) · zentiff · zenbitmaps · heic · zenraw · zenpdf · ultrahdr · mozjpeg-rs · webpx
Compression	zenflate · zenzop
Processing	zenresize · zenfilters · zenquant · zenblend
Metrics	zensim · fast-ssim2 · butteraugli · resamplescope-rs · codec-eval · codec-corpus
Pixel types & color	zenpixels · zenpixels-convert · linear-srgb · garb
Pipeline	zenpipe · zencodec · zencodecs · zenlayout · zennode
ImageResizer	ImageResizer (C#) — 24M+ NuGet downloads across all packages
Imageflow	Image optimization engine (Rust) — .NET · node · go — 9M+ NuGet downloads across all packages
Imageflow Server	The fast, safe image server (Rust+C#) — 552K+ NuGet downloads, deployed by Fortune 500s and major brands

* as of 2026

General Rust awesomeness

archmage · magetypes · enough · whereat · zenbench · cargo-copter

And other projects · GitHub @imazen · GitHub @lilith · lib.rs/~lilith · NuGet (over 30 million downloads / 87 packages)

License

Dual-licensed: AGPL-3.0 or commercial.

I've maintained and developed open-source image server software — and the 40+ library ecosystem it depends on — full-time since 2011. Fifteen years of continual maintenance, backwards compatibility, support, and the (very rare) security patch. That kind of stability requires sustainable funding, and dual-licensing is how we make it work without venture capital or rug-pulls. Support sustainable and secure software; swap patch tuesday for patch leap-year.

Our open-source products

Your options:

• Startup license — $1 if your company has under $1M revenue and fewer than 5 employees. Get a key →
• Commercial subscription — Governed by the Imazen Site-wide Subscription License v1.1 or later. Apache 2.0-like terms, no source-sharing requirement. Sliding scale by company size. Pricing & 60-day free trial →
• AGPL v3 — Free and open. Share your source if you distribute.

See LICENSE-COMMERCIAL for details.

Upstream code from memorysafety/rav1d is licensed under BSD-2-Clause. Our additions and improvements are dual-licensed (AGPL-3.0 or commercial) as above.

Upstream Contribution

We are willing to release our improvements under the original BSD-2-Clause license if upstream takes over maintenance of those improvements. We'd rather contribute back than maintain a parallel codebase. Open an issue or reach out.

Acknowledgments

Built on the work of the dav1d team (VideoLAN) and the rav1d team (ISRG/Prossimo). The original C and assembly implementations are exceptional — this fork demonstrates that safe Rust SIMD can get within 2x of hand-written assembly while eliminating entire classes of memory safety bugs.