konowebcodecs/docs/api.md

API

• createFFmpeg()
  • ffmpeg.load
  • ffmpeg.write
  • ffmpeg.writeText
  • ffmpeg.read
  • ffmpeg.remove
  • ffmpeg.transcode
  • ffmpeg.trim
  • ffmpeg.concatDemuxer
  • ffmpeg.run

---

createFFmpeg(options): ffmpeg

createFFmpeg is a factory function that creates a ffmpeg instance.

Arguments:

• options an object of customized options
  • corePath path for ffmpeg-core.js script
  • log a boolean to turn on all logs, default is false
  • logger a function to get log messages, a quick example is ({ message }) => console.log(message)
  • progress a function to trace the progress, a quick example is p => console.log(p)

Examples:

const { createFFmpeg } = FFmpeg;
const ffmpeg = createFFmpeg({
  corePath: "./node_modules/@ffmpeg/core/ffmpeg-core.js",
  log: true,
});

ffmpeg.load(): Promise

ffmpeg.load() loads ffmpeg-core.js script (download from remote if not presented), it makes WebAssembly code ready to use.

Examples:

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

ffmpeg.write(path, data): Promise

ffmpeg.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, File, Blob or base64 format

Examples:

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

ffmpeg.writeText(path, text): undefined

ffmpeg.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

Examples:

(async () => {
  ffmpeg.writeText("sub.srt", "...");
})();

ffmpeg.read(path): Uint8Array

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

Arguments:

• path path to read data from file system

Examples:

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

ffmpeg.remove(path): Promise

ffmpeg.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

Examples:

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

ffmpeg.ls(path): Promise

ffmpeg.ls() lists all files in specific path.

Arguments:

• path path to list

Examples:

(async () => {
  const dirs = ffmpeg.ls("/");
})();

ffmpeg.transcode(input, output, options): Promise

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

Arguments:

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

Examples:

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

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

ffmpeg.trim() trims video to specific interval.

Arguments:

• inputPath input file path, the input file should be written through ffmpeg.write()
• outputPath output file path, can be read with ffmpeg.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

Examples:

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

ffmpeg.concatDemuxer(input, output, options): Promise

ffmpeg.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 ffmpeg.write()
• output output file path, can be read with ffmpeg.read() later
• options a string to add extra arguments to ffmpeg

Examples:

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

ffmpeg.run(args): Promise

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

Arguments:

• args a string to represent arguments

Examples:

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