fix-webm-duration

navigator.mediaDevices.getUserMedia + MediaRecorder create WEBM files without duration metadata.

This library appends missing metadata section right to the file blob.

See the demo here.

Installation

Install from a package manager:

npm install @fix-webm-duration/fix

Then, the library could be imported:

import { fixWebmDuration } from "@fix-webm-duration/fix";

Usage

Syntax:

const newBlob = await fixWebmDuration(blob, duration, (options = {}));

where

• blob is Blob object with file contents from MediaRecorder
• duration is video duration in milliseconds (you should calculate it while recording the video)
• options is an object of options:
  • options.logger - a callback for logging debug messages or false. The callback should accept one argument - the message string. By default, console.debug will be used for logging. Passing false will disable the logging.

fixWebmDuration will parse and fix your file asynchronously and return the fixed blob once the result is ready.

If the original blob already contains duration metadata section and the duration value is not empty, the callback will receive it without any changes made.

Example:

let mediaRecorder;
let mediaParts;
let startTime;

function startRecording(stream: MediaStream, options: MediaRecorderOptions) {
    mediaParts = [];
    mediaRecorder = new MediaRecorder(stream, options);
    mediaRecorder.onstop = async () => {
        const duration = Date.now() - startTime;
        const buggyBlob = new Blob(mediaParts, { type: "video/webm" });

        const fixedBlob = await fixWebmDuration(buggyBlob, duration);
        displayResult(fixedBlob);
    };
    mediaRecorder.ondataavailable = (event) => {
        var data = event.data;
        if (data && data.size > 0) {
            mediaParts.push(data);
        }
    };
    mediaRecorder.start();
    startTime = Date.now();
}

function stopRecording() {
    mediaRecorder.stop();
}

function displayResult(blob: Blob) {
    // ...
}

Note: this example is not a MediaRecorder usage guide.