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由于本人需要原项目ffmpeg-worker-webm.js的视频帧截图功能,和ffmpeg-worker-mp4.js的获取video音频的功能,所以修改了Makefile的相关配置,并添加了GIF的解码功能。 最终生成文件如下:
ffmpeg-worker-mp4.js + ffmpeg-worker-mp4.wasm

原项目 readme如下:



This library provides FFmpeg builds ported to JavaScript using Emscripten project. Builds are optimized for in-browser use: minimal size for faster loading, asm.js, performance tunings, etc. Though they work in Node as well.


Currently available builds (additional builds may be added in future):

  • ffmpeg-webm.js - WebM encoding (VP8 & Opus encoders, popular decoders).
  • ffmpeg-worker-webm.js - Web Worker version of ffmpeg-webm.js.
  • ffmpeg-mp4.js - MP4 encoding (H.264 & AAC & MP3 encoders, popular decoders).
  • ffmpeg-worker-mp4.js - Web Worker version of ffmpeg-mp4.js.

Note: only NPM releases contain abovementioned files.

Version scheme

ffmpeg.js uses the following version pattern: major.minor.9ddd, where:

  • major - FFmpeg's major version number used in the builds.
  • minor - FFmpeg's minor version.
  • ddd - ffmpeg.js own patch version. Should not be confused with FFmpeg's patch version number.

Example: 2.7.9005


See documentation on Module object for the list of options that you can pass.

Sync run

ffmpeg.js provides common module API, ffmpeg-webm.js is the default module. Add its name after the slash if you need another build, e.g. require("ffmpeg.js/ffmpeg-mp4.js").

var ffmpeg = require("ffmpeg.js");
var stdout = "";
var stderr = "";
// Print FFmpeg's version.
  arguments: ["-version"],
  print: function(data) { stdout += data + "\n"; },
  printErr: function(data) { stderr += data + "\n"; },
  onExit: function(code) {
    console.log("Process exited with code " + code);

Use e.g. browserify in case of Browser.

Via Web Worker

ffmpeg.js also provides wrapper for main function with Web Worker interface to offload the work to a different process. Worker sends the following messages:

  • {type: "ready"} - Worker loaded and ready to accept commands.
  • {type: "run"} - Worker started the job.
  • {type: "stdout", data: "<line>"} - FFmpeg printed to stdout.
  • {type: "stderr", data: "<line>"} - FFmpeg printed to stderr.
  • {type: "exit", data: "<code>"} - FFmpeg exited.
  • {type: "done", data: "<result>"} - Job finished with some result.
  • {type: "error", data: "<error description>"} - Error occurred.

You can send the following messages to the worker:

  • {type: "run", ...opts} - Start new job with provided options.
var stdout = "";
var stderr = "";
var worker = new Worker("ffmpeg-worker-webm.js");
worker.onmessage = function(e) {
  var msg =;
  switch (msg.type) {
  case "ready":
    worker.postMessage({type: "run", arguments: ["-version"]});
  case "stdout":
    stdout += + "\n";
  case "stderr":
    stderr += + "\n";
  case "exit":
    console.log("Process exited with code " +;

This works in Browser as is, use e.g. webworker-threads Web Worker implementation in Node.


Empscripten supports several types of file systems. ffmpeg.js uses MEMFS to store the input/output files in FFmpeg's working directory. You need to pass Array of Object to MEMFS option with the following keys:

  • name (String) - File name, can't contain slashes.
  • data (ArrayBuffer/ArrayBufferView/Array) - File data.

ffmpeg.js resulting object has MEMFS option with the same structure and contains files which weren't passed to the input, i.e. new files created by FFmpeg.

var ffmpeg = require("ffmpeg.js");
var fs = require("fs");
var testData = new Uint8Array(fs.readFileSync("test.webm"));
// Encode test video to VP8.
var result = ffmpeg({
  MEMFS: [{name: "test.webm", data: testData}],
  arguments: ["-i", "test.webm", "-c:v", "libvpx", "-an", "out.webm"],
  // Ignore stdin read requests.
  stdin: function() {},
// Write out.webm to disk.
var out = result.MEMFS[0];
fs.writeFileSync(, Buffer(;

You can also mount other FS by passing Array of Object to mounts option with the following keys:

  • type (String) - Name of the file system.
  • opts (Object) - Underlying file system options.
  • mountpoint (String) - Mount path, must start with a slash, must not contain other slashes and also the following paths are blacklisted: /tmp, /home, /dev, /work. Mount directory will be created automatically before mount.

See documentation of FS.mount for more details.

var ffmpeg = require("ffmpeg.js");
  // Mount /data inside application to the current directory.
  mounts: [{type: "NODEFS", opts: {root: "."}, mountpoint: "/data"}],
  arguments: ["-i", "/data/test.webm", "-c:v", "libvpx", "-an", "/data/out.webm"],
  stdin: function() {},
// out.webm was written to the current directory.

Build instructions

Tips, use a docker container (basic ubuntu is good)

apt-get update
apt-get -y install wget python git automake libtool build-essential cmake libglib2.0-dev closure-compiler

cd /root # or /home/whatever
tar xzvf emsdk-portable.tar.gz
cd emsdk-portable
./emsdk update
./emsdk install latest
./emsdk activate latest
source ./

cd /root # or /home/whatever
git clone
cd ffmpeg.js
git submodule init
git submodule update --recursive

make all


Thanks to videoconverter.js for inspiration. And of course to all great projects which made this library possible: FFmpeg, Emscripten, asm.js, node.js and many others.


Own library code licensed under LGPL 2.1 or later.

WebM build

This build uses LGPL version of FFmpeg and thus available under LGPL 2.1 or later. See here for more details and FFmpeg's license information.

Included libraries:

See LICENSE.WEBM for the full text of software licenses used in this build.

MP4 build

This build uses GPL version of FFmpeg and thus available under GPL 2.0. It also includes patent encumbered H.264, AAC and MP3 encoders. Make sure to contact lawyer before using it in your country.

Included libraries:

See LICENSE.MP4 for the full text of software licenses used in this build.

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