How to reduce the length of a video using JavaScript? [closed]

Question

I am trying to trim the length of a video within the browser, from either the beginning or the end. What I currently have is a MediaStream which is being recorded using the MediaRecorder API, which I use to produce a Blob at the end of the recording with type set to 'video/mp4'. This works great and I am able to play the video back, however I would like a way to trim the video either at the start or end.

Upon further investigation of the MediaStream API I came across the SourceBuffer object, that you can obtain from a MediaStreamTrack and use it to remove a time slice, which is exactly what I want. However I am unsure of how to obtain the MediaStreamTrack from the video (blob) since video.srcObject property returns null.

Answer 1

I am trying to trim the length of a video within the browser, from either the beginning or the end.

You can use Array.prototype.slice() to remove blobs in chunks of one second 1000ms of data, or other time range, segments from end of array containing blobs pushed to an array at MediaRecorder dataavailable event. Where MediaRecorder .start() is called with parameter 1000, to set each recorded Blob to 1000ms of recorded data.

Approach utilizes modified version of https://github.com/samdutton/simpl/tree/gh-pages/mediarecorder . Added <input type="number"> elements to set remove chunks of 1s from recorded video for both playback and download by using .slice()

html

<video id="gum" autoplay muted controls></video>
<video id="recorded" autoplay controls></video>

<div>
  <button id="record">Start Recording</button><label for="record"></label><br>
  <span>Seconds of recorded video to play (min 1):</span><input min="1" type="number" disabled />
  <button id="play" disabled>Play</button>
  <span>Seconds of recorded video to download (min 1):</span><input min="1" type="number" disabled /><button id="download" disabled>Download</button>
</div>

javascript

'use strict';

/* globals MediaRecorder */

// This code is adapted from
// https://rawgit.com/Miguelao/demos/master/mediarecorder.html

'use strict';

/* globals MediaRecorder */

// This code is adapted from
// https://rawgit.com/Miguelao/demos/master/mediarecorder.html

var mediaSource = new MediaSource();
mediaSource.addEventListener('sourceopen', handleSourceOpen, false);
var mediaRecorder;
var recordedBlobs;
var sourceBuffer;
var gumVideo = document.querySelector('video#gum');
var recordedVideo = document.querySelector('video#recorded');
var input = document.querySelectorAll("input[type=number]");
recordedVideo.ontimeupdate = function(e) {
  console.log("recorded video currentTime:", e.target.currentTime)
}
gumVideo.onprogress = function(e) {
  // console.log("getUserMedia video currentTime:", e.target.currentTime)
}
var recordButton = document.querySelector('button#record');
var playButton = document.querySelector('button#play');
var downloadButton = document.querySelector('button#download');
recordButton.onclick = toggleRecording;
playButton.onclick = play;
downloadButton.onclick = download;

var currentTimes = [];
recordButton.nextElementSibling.innerHTML = "recorded video " 
                                            + currentTimes.length 
                                            + "s";
// window.isSecureContext could be used for Chrome
var isSecureOrigin = location.protocol === 'https:' ||
  location.host === 'localhost';
if (!isSecureOrigin) {
  alert('getUserMedia() must be run from a secure origin: HTTPS or localhost.' +
    '\n\nChanging protocol to HTTPS');
  location.protocol = 'HTTPS';
}

// Use old-style gUM to avoid requirement to enable the
// Enable experimental Web Platform features flag in Chrome 49

navigator.getUserMedia = navigator.getUserMedia ||
  navigator.webkitGetUserMedia || navigator.mozGetUserMedia;

var constraints = {
  audio: true,
  video: true
};

navigator.getUserMedia(constraints, successCallback, errorCallback);

function successCallback(stream) {
  console.log('getUserMedia() got stream: ', stream);
  window.stream = stream;
  if (window.URL) {
    gumVideo.src = window.URL.createObjectURL(stream);
  } else {
    gumVideo.src = stream;
  }
}

function errorCallback(error) {
  console.log('navigator.getUserMedia error: ', error);
}

// navigator.mediaDevices.getUserMedia(constraints)
// .then(function(stream) {
//   console.log('getUserMedia() got stream: ', stream);
//   window.stream = stream; // make available to browser console
//   if (window.URL) {
//     gumVideo.src = window.URL.createObjectURL(stream);
//   } else {
//     gumVideo.src = stream;
//   }
// }).catch(function(error) {
//   console.log('navigator.getUserMedia error: ', error);
// });

function handleSourceOpen(event) {
  console.log('MediaSource opened');
  sourceBuffer = mediaSource.addSourceBuffer('video/webm; codecs="vp8"');
  console.log('Source buffer: ', sourceBuffer);
}

function handleDataAvailable(event) {
  if (event.data && event.data.size > 0) {
    currentTimes.push(gumVideo.currentTime);
    recordedBlobs.push(event.data);
    recordButton.nextElementSibling.innerHTML = "recorded video " 
                                                + recordedBlobs.length 
                                                + "s";
  }
}

function handleStop(event) {
  console.log('Recorder stopped: ', event);
  console.log("recorded times from getUserMedia video:", currentTimes);
}

function toggleRecording() {
  if (recordButton.textContent === 'Start Recording') {
    startRecording();
  } else {
    stopRecording();
    recordButton.textContent = 'Start Recording';
    playButton.disabled = false;
    downloadButton.disabled = false;
  }
}

// The nested try blocks will be simplified when Chrome 47 moves to Stable
function startRecording() {
  var options = {
    mimeType: 'video/webm',
    bitsPerSecond: 100000
  };
  recordedBlobs = [];
  currentTimes = [];
  for (var i = 0; i < input.length; i++) {
    input[i].setAttribute("max", 1);
    input[i].setAttribute("disabled", "disabled");
  }
  playButton.disabled = true;
  downloadButton.disabled = true;
  try {
    mediaRecorder = new MediaRecorder(window.stream, options);
  } catch (e0) {
    console.log('Unable to create MediaRecorder with options Object: ', e0);
    try {
      options = {
        mimeType: 'video/webm,codecs=vp9',
        bitsPerSecond: 100000
      };
      mediaRecorder = new MediaRecorder(window.stream, options);
    } catch (e1) {
      console.log('Unable to create MediaRecorder with options Object: ', e1);
      try {
        options = 'video/vp8'; // Chrome 47
        mediaRecorder = new MediaRecorder(window.stream, options);
      } catch (e2) {
        alert('MediaRecorder is not supported by this browser.\n\n' +
          'Try Firefox 29 or later, or Chrome 47 or later,'
          + ' with Enable experimental Web Platform features enabled '
          + ' from chrome://flags.');
        console.error('Exception while creating MediaRecorder:', e2);
        return;
      }
    }
  }
  console.log('Created MediaRecorder', mediaRecorder, 'with options', options);
  recordButton.textContent = 'Stop Recording';
  playButton.disabled = true;
  downloadButton.disabled = true;
  mediaRecorder.onstop = handleStop;
  mediaRecorder.ondataavailable = handleDataAvailable;
  mediaRecorder.start(1000); // collect 1000ms of data
  console.log('MediaRecorder started', mediaRecorder);
}

function stopRecording() {
  mediaRecorder.stop();
  for (var i = 0; i < input.length; i++) {
    input[i].setAttribute("max", recordedBlobs.length);
    input[i].removeAttribute("disabled");
  }
  console.log('Recorded Blobs: ', recordedBlobs);
  recordedVideo.controls = true;
}

function play() {
  console.log(`playing ${input[0].value}s of getUserMedia video` 
             + `recorded by MediaRecorder from time ranges`
             , currentTimes.slice(0, input[0].value));
  // slice `input[0].value` amount, in seconds, from end of recorded video
  // for playback
  var file = recordedBlobs.slice(0, input[0].value);
  var superBuffer = new Blob(file, {
    type: 'video/webm'
  });
  recordedVideo.src = window.URL.createObjectURL(superBuffer);
}

function download() {
    // slice `input[1].value` amount, in seconds, from end of recorded video
    // for download
  var file = recordedBlobs.slice(0, input[1].value);
  var blob = new Blob(file, {
    type: 'video/webm'
  });
  var url = window.URL.createObjectURL(blob);
  var a = document.createElement('a');
  a.style.display = 'none';
  a.href = url;
  a.download = 'test.webm';
  document.body.appendChild(a);
  a.click();
  setTimeout(function() {
    document.body.removeChild(a);
    window.URL.revokeObjectURL(url);
  }, 100);
}

plnkr https://plnkr.co/edit/LxuV5jMX0RZtDxOxT1qa?p=preview