The last mile from encoder to playable MP4.

cargo add muxide

Muxide takes correctly-timestamped, already-encoded audio/video frames and produces a standards-compliant MP4 — pure Rust, minimal external dependencies, no FFmpeg.

Why Muxide Exists

If you're building a recording pipeline in Rust, you know the tradeoffs:

Muxide solves one job cleanly:

Take already-encoded frames with correct timestamps → produce a standards-compliant, immediately-playable MP4 → using pure Rust.

Nothing more. Nothing less.

Installation & Usage

As a Library

cargo add muxide

use muxide::api::{MuxerBuilder, VideoCodec};

let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::H264, 1920, 1080, 30.0)?
    .build()?;

// Write your encoded frames...
muxer.write_video(0.0, &h264_frame, true)?;
muxer.finish()?;

As a CLI Tool

# Install globally
cargo install muxide

# Or download pre-built binary from releases
# Then use:
muxide --help

# Quick examples:
muxide mux --video frames/ --output output.mp4 --width 1920 --height 1080 --fps 30
muxide mux --video video.h264 --audio audio.aac --output output.mp4
muxide validate --video frames/ --audio audio.aac
muxide info input.mp4

The CLI tool accepts raw encoded frames from stdin or files and produces MP4 output.

Core Invariant

Muxide enforces a strict contract:

If input violates the contract, Muxide fails fast with explicit errors—no silent corruption, no guessing.

Features

Design Principles

Note: no_std is not supported. Muxide requires std::io::Write.

Quick Start

use muxide::api::{MuxerBuilder, VideoCodec, AudioCodec, Metadata};
use std::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let file = File::create("recording.mp4")?;
    
    let mut muxer = MuxerBuilder::new(file)
        .video(VideoCodec::H264, 1920, 1080, 30.0)
        .audio(AudioCodec::Aac, 48000, 2)
        .with_metadata(Metadata::new().with_title("My Recording"))
        .with_fast_start(true)
        .build()?;

    // Write encoded frames (from your encoder)
    // muxer.write_video(pts_seconds, h264_annex_b_bytes, is_keyframe)?;
    // muxer.write_audio(pts_seconds, aac_adts_bytes)?;

    let stats = muxer.finish_with_stats()?;
    println!("Wrote {} frames, {} bytes", stats.video_frames, stats.bytes_written);
    Ok(())
}

// Requires VPS, SPS, PPS in first keyframe
let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::H265, 3840, 2160, 30.0)
    .build()?;
muxer.write_video(0.0, &hevc_annexb_with_vps_sps_pps, true)?;

// Requires Sequence Header OBU in first keyframe
let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::Av1, 1920, 1080, 60.0)
    .build()?;
muxer.write_video(0.0, &av1_obu_with_sequence_header, true)?;

// Opus always uses 48kHz internally (per spec)
let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::H264, 1920, 1080, 30.0)
    .audio(AudioCodec::Opus, 48000, 2)
    .build()?;
muxer.write_audio(0.0, &opus_packet)?;

use muxide::codec::vp9::Vp9Config;

// H.264
let sps_bytes = vec![0x67, 0x42, 0x00, 0x1e, 0xda, 0x02, 0x80, 0x2d, 0x8b, 0x11];
let pps_bytes = vec![0x68, 0xce, 0x38, 0x80];

let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::H264, 1920, 1080, 30.0)
    .with_sps(sps_bytes)
    .with_pps(pps_bytes)
    .new_with_fragment()?;

// H.265
let vps_bytes = vec![0x40, 0x01, 0x0c, 0x01, 0xff, 0xff, 0x01, 0x60, 0x00];
let sps_bytes = vec![0x42, 0x01, 0x01, 0x01, 0x60, 0x00, 0x00, 0x03, 0x00, 0x90, 0x00];
let pps_bytes = vec![0x44, 0x01, 0xc0, 0x73, 0xc0, 0x4c, 0x90];

let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::H265, 1920, 1080, 30.0)
    .with_vps(vps_bytes)
    .with_sps(sps_bytes)
    .with_pps(pps_bytes)
    .new_with_fragment()?;

// AV1
let seq_header_bytes = vec![
    0x0A, 0x10, // OBU header + size (example)
    0x00, 0x00, 0x00, 0x00,
];

let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::Av1, 1920, 1080, 30.0)
    .with_av1_sequence_header(seq_header_bytes)
    .new_with_fragment()?;

// VP9
let vp9_config = Vp9Config {
    width: 1920,
    height: 1080,
    profile: 0,
    bit_depth: 8,
    color_space: 0,
    transfer_function: 0,
    matrix_coefficients: 0,
    level: 0,
    full_range_flag: 0,
};

let mut muxer = MuxerBuilder::new(file)
    .video(VideoCodec::Vp9, 1920, 1080, 30.0)
    .with_vp9_config(vp9_config)
    .new_with_fragment()?;

// Get init segment (ftyp + moov)
let init_segment = muxer.init_segment();

// Write frames...
muxer.write_video(0, 0, &frame, true)?;

// Get media segments (moof + mdat)
if let Some(segment) = muxer.flush_segment() {
    // Send segment to client
}

// When encoder produces B-frames, provide both PTS and DTS
muxer.write_video_with_dts(
    pts_seconds,  // Presentation timestamp
    dts_seconds,  // Decode timestamp (for B-frame ordering)
    &frame_data,
    is_keyframe
)?;

Command Line Tool

Muxide includes a command-line tool for quick testing and development workflows:

# Install the CLI tool
cargo install muxide

# Basic video-only muxing
muxide mux \
  --video keyframes.h264 \
  --width 1920 --height 1080 --fps 30 \
  --output recording.mp4

# Video + audio with metadata
muxide mux \
  --video stream.h264 \
  --audio stream.aac \
  --video-codec h264 \
  --audio-codec aac-he \
  --width 1920 --height 1080 --fps 30 \
  --sample-rate 44100 --channels 2 \
  --title "My Recording" \
  --language eng \
  --output final.mp4

# JSON output for automation
muxide mux --json [args...] > stats.json

# Validate input files without muxing
muxide validate --video input.h264 --audio input.aac

# Get info about supported codecs
muxide info

Supported Codecs:

• Video: H.264 (AVC), H.265 (HEVC), AV1
• Audio: AAC (all profiles), Opus

Features:

• Progress reporting with --verbose
• JSON output for CI/CD integration
• Comprehensive error messages
• Fast-start MP4 layout by default
• Metadata support (title, language, creation time)

What Muxide Is Not

Muxide is intentionally focused. It does not:

Muxide is the last mile: encoder output → playable file.

Use Cases

Muxide is a great fit for:

• 🎥 Screen recorders — capture → encode → mux → ship
• 📹 Camera apps — webcam/IP camera recording pipelines (e.g., CrabCamera integration)
• 🎬 Video editors — export timeline to MP4
• 📡 Streaming — generate fMP4 segments for DASH/HLS
• 🏭 Embedded systems — single binary, no external deps
• 🔬 Scientific apps — deterministic, reproducible output

Probably not a fit if you need encoding, demuxing, or legacy codecs (MPEG-2, etc.).

Example: Fast-Start Proof

The faststart_proof example demonstrates a structural MP4 invariant:

• Two MP4 files are generated from the same encoded inputs
• One with fast-start enabled, one without
• No external tools are used at any stage

$ cargo run --example faststart_proof --release

output: recording_faststart.mp4
    layout invariant: moov before mdat = YES

output: recording_normal.mp4
    layout invariant: moov before mdat = NO

When served over HTTP, the fast-start file can begin playback without waiting for the full download (player behavior varies, but the layout property is deterministic).

This example is intentionally minimal:

• Timestamps are generated in-code
• No B-frames/DTS paths are exercised
• The goal is container layout correctness, not encoding quality

Performance

Muxide is designed for minimal overhead. Muxing should never be your bottleneck.

Note: Benchmarks are based on development hardware. Encoding is typically the bottleneck—muxing overhead is negligible. Run cargo bench for your environment (dev-only benchmarks available).AVC

• Format: Annex B (start codes: 00 00 00 01 or 00 00 01)
• First keyframe must contain: SPS and PPS NAL units
• NAL unit types: IDR (keyframe), non-IDR, SPS, PPS

H.265/HEVC

• Format: Annex B (start codes)
• First keyframe must contain: VPS, SPS, and PPS NAL units
• NAL unit types: IDR_W_RADL, IDR_N_LP, CRA, VPS, SPS, PPS

AV1

• Format: OBU (Open Bitstream Unit) stream
• First keyframe must contain: Sequence Header OBU
• OBU types: Sequence Header, Frame, Frame Header, Tile Group

AAC

• Format: ADTS (Audio Data Transport Stream)
• Header: 7-byte ADTS header per frame
• Profiles: LC-AAC recommended

Opus

• Format: Raw Opus packets (no container)
• Sample rate: Always 48000 Hz (Opus specification)
• Channels: 1 (mono) or 2 (stereo)

Documentation

FAQ

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.

Muxide is designed to be boring in the best way:
predictable, strict, fast, and invisible once integrated.