#multimedia #encoding #video


Idiomatic bindings for OpenH264

14 releases

0.2.8 Sep 29, 2021
0.2.7 Sep 28, 2021
0.1.17 Sep 22, 2021
0.0.0 Sep 1, 2018

#2 in Video

Download history 1/week @ 2021-07-16 3/week @ 2021-07-30 1/week @ 2021-08-13 87/week @ 2021-09-03 12/week @ 2021-09-10 19/week @ 2021-09-17 99/week @ 2021-09-24 96/week @ 2021-10-01 31/week @ 2021-10-08

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97K SLoC

C++ 50K SLoC // 0.1% comments Assembly 21K SLoC // 0.1% comments GNU Style Assembly 12K SLoC // 0.2% comments C 9K SLoC // 0.1% comments Rust 2.5K SLoC // 0.0% comments Visual Studio Project 835 SLoC Shell 23 SLoC Batch 11 SLoC

Latest Version docs BSD-2 Rust Rust

OpenH264 Rust API

Idiomatic and low-level bindings for OpenH264, converting between these two in Rust:


Example API

Decode some H.264 bitstream to YUV:

use openh264::decoder::Decoder;
use openh264::nal_units;

let h264_in = include_bytes!("../tests/data/multi_512x512.h264");
let mut decoder = Decoder::new()?;

// Split H.264 into NAL units and decode each.
for packet in nal_units(h264_in) {
    let yuv = decoder.decode(packet)?;

And encode the same YUV back to H.264:

use openh264::encoder::{Encoder, EncoderConfig};

let config = EncoderConfig::new(512, 512);
let mut encoder = Encoder::with_config(config)?;

// Encode YUV back into H.264.
let bitstream = encoder.encode(&yuv)?;

Platform Support

Test results on various platforms:

Platform Compiled Unit Tested
aarch64-linux-android 🆗1 -
wasm32-unknown-unknown 1,2 -

✅ works out of the box; 🆗 the usual shenanigans required; ❌ not supported.

1 via cargo build --target <platform>, needs CXX set and libc++_shared.so.
2 unclear if could ever work, investigation welcome


Tested on a i9-9900K, Windows 10, single threaded de- and encoding:

-- Default --
test decode_yuv_single_1920x1080     ... bench:   9,243,380 ns/iter (+/- 497,200)
test decode_yuv_single_512x512_cabac ... bench:   1,841,775 ns/iter (+/- 53,211)
test decode_yuv_single_512x512_cavlc ... bench:   2,076,030 ns/iter (+/- 7,287)
test encode_1920x1080_from_yuv       ... bench:  38,657,620 ns/iter (+/- 793,310)
test encode_512x512_from_yuv         ... bench:   6,420,605 ns/iter (+/- 1,003,485)

-- Feature `asm` --
test decode_yuv_single_1920x1080     ... bench:   4,265,260 ns/iter (+/- 89,438)
test decode_yuv_single_512x512_cabac ... bench:     901,025 ns/iter (+/- 21,902)
test decode_yuv_single_512x512_cavlc ... bench:   1,618,880 ns/iter (+/- 53,713)
test encode_1920x1080_from_yuv       ... bench:  13,455,160 ns/iter (+/- 862,042)
test encode_512x512_from_yuv         ... bench:   4,011,700 ns/iter (+/- 2,094,471)

-- Color Conversion --
test convert_yuv_to_rgb_1920x1080    ... bench:   7,226,290 ns/iter (+/- 110,871)
test convert_yuv_to_rgb_512x512      ... bench:     907,340 ns/iter (+/- 28,296)

Compile Features

  • decoder - Enable the decoder. Used by default.
  • encoder - Enable the encoder. Used by default.
  • backtrace - Enable backtraces on errors (requires nightly)
  • asm - Enable assembly. Only supported on x86 and ARM, requires nasm installed.


  • How does openh264-sys2 differ from openh264-sys?

    We directly ship OpenH264 source code and provide simple, hand-crafted compilation via cc in build.rs. Ouropenh264-sys2 crate should compile via cargo build out of the box on most platforms, and cross-compile via cargo build --target ... as long as the environment variable CXX is properly set.

  • I need to fix an important OpenH264 security hole, how can I update the library?

    Cisco's OpenH264 library is contained in openh264-sys2/upstream. Updating is (almost, see below) as simple as pulling their latest source, copying it into that directory, and manually removing all "resource" files. We probably should have a script to strip that folder automatically ...

  • I heard Rust is super-safe, will this make decoding my videos safe too?

    No. Below a thin Rust layer we rely on a very complex C library, and an equally complex standard. Apart from Rust being a much nicer language to work with, depending on this project will give you no additional safety guarantees as far as video handling is concerned. FYI, this is not making a statement about OpenH264, but about the realities of securing +50k lines of C against attacks.

  • Feature X is missing or broken, will you fix it?

    Right now I only have time to implement what I need. However, I will gladly accept PRs either extending the APIs, or fixing bugs; see below.

  • Decoder::decode() returned an error, is this a bug?

    Maybe. Probably not. Some encoders can write data OpenH264 doesn't understand, and if all frames fail this could either be your encoder doing exotic things, OpenH264 not having implemented a certain feature, or us having a bug.

    However, if only some frames fail the most likely reasons are your endoder injecting some special packets or simply transmission errors. In other words, unless you have a very controlled setup you simply should not terminate on the first error(s), but simply continue decoding and hope for the decoder to recover.

    FWIW, we consider OpenH264's h264dec the reference decoder. If you can get it to emit YUV for some input then it would be a bug if we can't. However, any stream / frame it fails on is pretty much a wontfix for us.

OpenH264 Patches Applied

Ideally the embedded upstream should be pristine. That said, the following patches have been applied to fix Valgrind issues and crashes on some platforms:

  • decoder.cpp - removed if (pCtx->pDstInfo) pCtx->pDstInfo->iBufferStatus = 0; which seems to write to previously deallocated memory.

Help with upstreaming them would be appreciated.


PRs are very welcome. Feel free to submit PRs and fixes right away. You can open issues if you want to discuss things, but due to time restrictions on my side the project will have to rely on people contributing.

Especially needed:

  • BT.601 / BT.709 YUV <-> RGB Conversion
  • Faster YUV to RGB conversion
  • Have script to automatically update / import OpenH264 source (or submodule?)
  • WASM investigation (either patch, or evidence it can't be fixed)
  • Submit patches upstream
  • Feedback which platforms successfully built on


  • v0.2 - Added encoder; asm feature for 2x - 3x speed boost.
  • v0.1 - Initial release, decoder only.


  • OpenH264 core library is BSD-2, Cisco.
  • Wrapper code is BSD-2, Ralf Biedert.