splica

A modern media processing library and CLI, built in Rust. Covers the 90% of video/audio workloads that matter — with memory safety, a sane API, and single-binary distribution.

Why

ffmpeg is indispensable. It's also a C codebase from 2000 with a cryptic CLI, an unsafe API, and a constant stream of memory corruption CVEs. Every service that accepts user-uploaded video is exposed.

splica takes a different approach:

	ffmpeg	splica
Language	C + hand-written Assembly	Rust (unsafe confined to FFI boundaries)
CLI	Cryptic flag soup	Structured subcommands with helpful errors
Library API	Opaque structs, negative int error codes, manual lifecycle management	Typed builders, Result<T, E>, ownership-driven resource management
Distribution	Shared library hell	cargo install splica
Browser	Painful WASM port	First-class WASM target
Format coverage	Everything ever invented	H.264, H.265, AV1, AAC, Opus in MP4, WebM, MKV

splica does not aim to replace ffmpeg for every use case. If you need to transcode Sega Dreamcast video captures or mux RealMedia streams, ffmpeg is your tool. If you're building a product that processes video in 2026, splica is.

CLI

# Transcode to H.265, keep audio
splica transcode input.mp4 -c:v h265 -o output.mp4

# Extract audio as Opus
splica extract audio input.mp4 -c opus -o output.ogg

# Scale and trim
splica transcode input.mp4 \
  --scale 1280x720 \
  --trim 00:01:30..00:04:00 \
  -o output.mp4

# Probe container info
splica probe input.mp4

# Concatenate multiple files
splica concat part1.mp4 part2.mp4 part3.mp4 -o full.mp4

# HLS packaging for streaming
splica package input.mp4 --format hls --segment-duration 6 -o output/

Errors tell you what went wrong and how to fix it:

Error: Unsupported codec 'vp8' for container 'mp4'

  MP4 containers support: H.264, H.265, AV1
  VP8 is supported in: WebM

  Try: splica transcode input.mp4 -c:v vp8 -o output.webm

Library API

Basic transcoding

use splica::{Pipeline, Codec, Container};

let pipeline = Pipeline::open("input.mp4")?
    .video(|v| v.codec(Codec::H265).bitrate("4M"))
    .audio(|a| a.codec(Codec::Opus).bitrate("128k"))
    .output(Container::Mp4)
    .build()?;

pipeline.run("output.mp4")?;

Filter graph

use splica::{Pipeline, filters};

let pipeline = Pipeline::open("input.mp4")?
    .video(|v| {
        v.filter(filters::Scale::new(1280, 720))
         .filter(filters::Trim::new("00:01:30".."00:04:00"))
    })
    .build()?;

pipeline.run("output.mp4")?;

Probing

use splica::probe;

let info = probe("input.mp4")?;
println!("Duration: {}", info.duration());
for track in info.tracks() {
    println!("  {} — {} {}", track.index(), track.codec(), track.kind());
}

Low-level: reading packets

use splica::mp4::Mp4Demuxer;

let mut demuxer = Mp4Demuxer::open("input.mp4")?;
for track in demuxer.tracks() {
    println!("Track {}: {} {:?}", track.index(), track.codec(), track.resolution());
}

while let Some(packet) = demuxer.read_packet()? {
    println!("Track {} | pts={} | {} bytes", packet.track, packet.pts, packet.data.len());
}

Supported Formats

Containers

Format	Demux	Mux
MP4 (ISO BMFF)	Yes	Yes
WebM	Yes	Yes
MKV	Yes	Yes

Video Codecs

Codec	Decode	Encode	Backend
H.264	Yes	Yes	openh264 (FFI)
H.265/HEVC	Yes	Planned	FFI
AV1	Yes	Yes	dav1d (decode, FFI), rav1e (encode, pure Rust)

Audio Codecs

Codec	Decode	Encode	Backend
AAC	Yes	Yes	fdk-aac (FFI)
Opus	Yes	Yes	libopus (FFI)

Building from Source

git clone https://github.com/TODO/splica.git
cd splica
cargo build --release

The binary is at target/release/splica.

Feature Flags

# Minimal build (MP4 demux only, no codecs)
cargo build --no-default-features

# Full build with all codecs
cargo build --features full

# Specific codecs
cargo build --features "h264,av1,opus"

Exit Codes

splica uses structured exit codes for automation. See docs/exit-codes.md for the full contract, including JSON error_kind mapping and retry guidance.

Code	Meaning	Retryable
0	Success	N/A
1	Bad input (malformed file, unsupported format, invalid arguments)	No
2	Internal error (encoder/muxer/I/O failure)	Yes
3	Resource exhausted (memory, file handles, budget limits)	Yes

Documentation

• Scope -- what splica is and is not, and when to use ffmpeg instead
• Exit Codes -- exit code contract for automation consumers
• Stability Policy -- semver guarantees and what counts as a breaking change
• API Guide -- using splica as a Rust library

Project Status

splica is in early development. The API is unstable and will change. See the stability policy for details on what will be guaranteed after 1.0.

License

Licensed under the Apache License, Version 2.0. See LICENSE for details.