konowebcodecs/docs/api.md

API

• createWorker()
  • Worker.load
  • Worker.write
  • Worker.writeText
  • Worker.read
  • Worker.remove
  • Worker.transcode
  • Worker.trim
  • Worker.concatDemuxer
  • Worker.run

---

createWorker(options): Worker

createWorker is a factory function that creates a ffmpeg worker, a worker is basically a Web Worker in browser and Child Process in Node.

Arguments:

• options an object of customized options
  • corePath path for ffmpeg-core.js script
  • workerPath path for downloading worker script
  • workerBlobURL a boolean to define whether to use Blob URL for worker script, default: true
  • logger a function to log the progress, a quick example is m => console.log(m)
  • progress a function to trace the progress, a quick example is p => console.log(p)

Examples:

const { createWorker } = FFmpeg;
const worker = createWorker({
  corePath: "./node_modules/@ffmpeg/core/ffmpeg-core.js",
  logger: m => console.log(m)
});

Worker.load(jobId): Promise

Worker.load() loads ffmpeg-core.js script (download from remote if not presented), it makes Web Worker/Child Process ready for next action.

Arguments:

• jobId jobId is generated by ffmpeg.js to identify each job, but you can put your own when calling the function.

Examples:

(async () => {
  await worker.load();
})();

Worker.write(path, data, jobId): Promise

Worker.write() writes data to specific path in Emscripten file system, it is an essential step before doing any other tasks.

Currently we found an issue that you should not have parallel Worker.write() as it may cause unexpected behavior, please do it in sequential for-loop like HERE

Arguments:

• path path to write data to file system
• data data to write, can be Uint8Array, URL or base64 format
• jobId @see Worker.load()

Examples:

(async () => {
  await worker.write(
    "flame.avi",
    "http://localhost:3000/tests/assets/flame.avi"
  );
})();

Worker.writeText(path, text, jobId): Promise

Worker.write() writes text data to specific path in Emscripten file system.

Arguments:

• path path to write data to file system
• text string to write to file
• jobId @see Worker.load()

Examples:

(async () => {
  await worker.write("sub.srt", "...");
})();

Worker.read(path, jobId): Promise

Worker.read() reads data from file system, often used to get output data after specific task.

Arguments:

• path path to read data from file system
• jobId @see Worker.load()

Examples:

(async () => {
  const { data } = await worker.read("output.mp4");
})();

Worker.remove(path, jobId): Promise

Worker.remove() removes files in file system, it will be better to delete unused files if you need to run ffmpeg.js multiple times.

Arguments:

• path path for file to delete
• jobId @see Worker.load()

Examples:

(async () => {
  await worker.remove("output.mp4");
})();

Worker.transcode(input, output, options, jobId): Promise

Worker.transcode() transcode a video file to another format.

Arguments:

• input input file path, the input file should be written through Worker.write()
• output output file path, can be read with Worker.read() later
• options a string to add extra arguments to ffmpeg
• jobId @see Worker.load()

Examples:

(async () => {
  await worker.transcode("flame.avi", "output.mp4", "-s 1920x1080");
})();

Worker.trim(input, output, from, to, options, jobId): Promise

Worker.trim() trims video to specific interval.

Arguments:

• inputPath input file path, the input file should be written through Worker.write()
• outputPath output file path, can be read with Worker.read() later
• from start time, can be in time stamp (00:00:12.000) or seconds (12)
• to end time, rule same as above
• options a string to add extra arguments to ffmpeg
• jobId @see Worker.load()

Examples:

(async () => {
  await worker.trim("flame.avi", "output.mp4", 1, 2);
})();

Worker.concatDemuxer(input, output, options, jobId): Promise

Worker.concatDemuxer() concatenates multiple videos using concatDemuxer. This method won't encode the videos again. But it has its limitations. See Concat demuxer Wiki

Arguments:

• input input file paths as an Array, the input files should be written through Worker.write()
• output output file path, can be read with Worker.read() later
• options a string to add extra arguments to ffmpeg
• jobId check Worker.load()

Examples:

(async () => {
  await worker.concatDemuxer(["flame-1.avi", "flame-2.avi"], "output.mp4");
})();

If the input video files are the same as the output video file, you can pass an extra option to speed up the process

(async () => {
  await worker.concatDemuxer(["flame-1.mp4", "flame-2.mp4"], "output.mp4", "-c copy");
})();

Worker.run(args, jobId): Promise

Worker.run() is similar to FFmpeg cli tool, aims to provide maximum flexiblity for users.

Arguments:

• args a string to represent arguments
• jobId check Worker.load()

Examples:

(async () => {
  await worker.run("-i flame.avi -s 1920x1080 output.mp4");
})();