How to use MediaRecorder as MediaSource

Question

As an exercise in learning WebRTC I am trying to to show the local webcam and side by side with a delayed playback of the webcam. In order to achieve this I am trying to pass recorded blobs to a BufferSource and use the corresponding MediaSource as source for a video element.

// the ondataavailable callback for the MediaRecorder
async function handleDataAvailable(event) {
  // console.log("handleDataAvailable", event);
  if (event.data && event.data.size > 0) {
    recordedBlobs.push(event.data);
  }

  if (recordedBlobs.length > 5) {
    if (recordedBlobs.length === 5)
      console.log("buffered enough for delayed playback");
    if (!updatingBuffer) {
      updatingBuffer = true;
      const bufferedBlob = recordedBlobs.shift();
      const bufferedAsArrayBuffer = await bufferedBlob.arrayBuffer();
      if (!sourceBuffer.updating) {
        console.log("appending to buffer");
        sourceBuffer.appendBuffer(bufferedAsArrayBuffer);
      } else {
        console.warn("Buffer still updating... ");
        recordedBlobs.unshift(bufferedBlob);
      }
    }
  }
}

// connecting the media source to the video element
recordedVideo.src = null;
recordedVideo.srcObject = null;
recordedVideo.src = window.URL.createObjectURL(mediaSource);
recordedVideo.controls = true;
try {
  await recordedVideo.play();
} catch (e) {
  console.error(`Play failed: ${e}`);
}

All code: https://jsfiddle.net/43rm7258/1/

When I run this in Chromium 78 I get an NotSupportedError: Failed to load because no supported source was found. from the play element of the video element.

I have no clue what I am doing wrong or how to proceed at this point.

This is about something similar, but does not help me: MediaSource randomly stops video

This example was my starting point: https://webrtc.github.io/samples/src/content/getusermedia/record/

Answer 1

In Summary

Getting it to work in Firefox and Chrome is easy: you just need to add an audio codec to your codecs list! video/webm;codecs=opus,vp8

Getting it to work in Safari is significantly more complicated. MediaRecorder is an "experimental" feature that has to be manually enabled under the developer options. Once enabled, Safari lacks an isTypeSupported method, so you need to handle that. Finally, no matter what you request from the MediaRecorder, Safari will always hand you an MP4 file - which cannot be streamed the way WEBM can. This means you need to perform transmuxing in JavaScript to convert the video container format on the fly

Android should work if Chrome works

iOS does not support Media Source Extensions, so SourceBuffer is not defined on iOS and the whole solution will not work

Original Post

Looking at the JSFiddle you posted, one quick fix before we get started:

• You reference a variable errorMsgElement which is never defined. You should add a <div> to the page with an appropriate ID and then create a const errorMsgElement = document.querySelector(...) line to capture it

Now something to note when working with Media Source Extensions and MediaRecorder is that support is going to be very different per browser. Even though this is a "standardized" part of the HTML5 spec, it's not very consistent across platforms. In my experience getting MediaRecorder to work in Firefox doesn't take too much effort, getting it to work in Chrome is a bit harder, getting it to work in Safari is damned-near impossible, and getting it to work on iOS is literally not something you can do.

I went through and debugged this on a per-browser basis and recorded my steps, so that you can understand some of the tools available to you when debugging media issues

Firefox

When I checked out your JSFiddle in Firefox, I saw the following error in the console:

NotSupportedError: An audio track cannot be recorded: video/webm;codecs=vp8 indicates an unsupported codec

I recall that VP8 / VP9 were big pushes by Google and as such may not work in Firefox, so I tried making one small tweak to your code. I removed the , options) parameter from your call to new MediaRecorder(). This tells the browser to use whatever codec it wants, so you will likely get different output in every browser (but it should at least work in every browser)

This worked in Firefox, so I checked out Chrome.

Chrome

This time I got a new error:

(index):409 Uncaught (in promise) DOMException: Failed to execute 'appendBuffer' on 'SourceBuffer': This SourceBuffer has been removed from the parent media source. at MediaRecorder.handleDataAvailable (https://fiddle.jshell.net/43rm7258/1/show/:409:22)

So I headed over to chrome://media-internals/ in my browser and saw this:

Audio stream codec opus doesn't match SourceBuffer codecs.

In your code you're specifying a video codec (VP9 or VP8) but not an audio codec, so the MediaRecorder is letting the browser choose any audio codec it wants. It looks like in Chrome's MediaRecorder by default chooses "opus" as the audio codec, but Chrome's SourceBuffer by default chooses something else. This was trivially fixed. I updated your two lines that set the options.mimeType like so:

• options = { mimeType: "video/webm;codecs=opus, vp9" };
• options = { mimeType: "video/webm;codecs=opus, vp8" };

Since you use the same options object for declaring the MediaRecorder and the SourceBuffer, adding the audio codec to the list means the SourceBuffer is now declared with a valid audio codec and the video plays

For good measure I tested the new code (with an audio codec) on Firefox. This worked! So we're 2 for 2 just by adding the audio codec to the options list (and leaving it in the parameters for declaring the MediaRecorder)

It looks like VP8 and opus work in Firefox, but aren't the defaults (although unlike Chrome, the default for MediaRecorder and SourceBuffer are the same, which is why removing the options parameter entirely worked)

Safari

This time we got an error that we may not be able to work through:

Unhandled Promise Rejection: ReferenceError: Can't find variable: MediaRecorder

The first thing I did was Google "Safari MediaRecorder", which turned up this article. I thought I'd give it a try, so I took a look. Sure enough:

I clicked on this to enable MediaRecorder and was met with the following in the console:

Unhandled Promise Rejection: TypeError: MediaRecorder.isTypeSupported is not a function. (In 'MediaRecorder.isTypeSupported(options.mimeType)', 'MediaRecorder.isTypeSupported' is undefined)

So Safari doesn't have the isTypeSupported method. Not to worry, we'll just say "if this method doesn't exist, assume it's Safari and set the type accordingly"

  if (MediaRecorder.isTypeSupported) {
    options = { mimeType: "video/webm;codecs=vp9" };
    if (!MediaRecorder.isTypeSupported(options.mimeType)) {
      console.error(`${options.mimeType} is not Supported`);
      errorMsgElement.innerHTML = `${options.mimeType} is not Supported`;
      options = { mimeType: "video/webm;codecs=vp8" };
      if (!MediaRecorder.isTypeSupported(options.mimeType)) {
        console.error(`${options.mimeType} is not Supported`);
        errorMsgElement.innerHTML = `${options.mimeType} is not Supported`;
        options = { mimeType: "video/webm" };
        if (!MediaRecorder.isTypeSupported(options.mimeType)) {
          console.error(`${options.mimeType} is not Supported`);
          errorMsgElement.innerHTML = `${options.mimeType} is not Supported`;
          options = { mimeType: "" };
        }
      }
    }
  } else {
    options = { mimeType: "" };
  }

Now I just had to find a mimeType that Safari supported. Some light Googling suggests that H.264 is supported, so I tried:

options = { mimeType: "video/webm;codecs=h264" };

This successfully gave me MediaRecorder started, but failed at the line addSourceBuffer with the new error:

NotSupportedError: The operation is not supported.

I will continue to try and diagnose how to get this working in Safari, but for now I've at least addresses Firefox and Chrome

Update 1

I've continued to work on Safari. Unfortunately Safari lacks the tooling of Chrome and Firefox to dig deep into media internals, so there's a lot of guesswork involved.

I had previously figured out that we were getting an error "The operation is not supported" when trying to call addSourceBuffer. So I created a one-off page to try and call just this method under different circumstances:

• Maybe add a source buffer before play is called on the video
• Maybe add a source buffer before the media source has been attached to a video element
• Maybe add a source buffer with different codecs
• etc

I found that the issue was the codec still, and that the error messaging about the "operation" not being permitted was slightly misleading. It was the parameters that were not permitted. Simply supplying "h264" worked for the MediaRecorder, but the SourceBuffer needed me to pass along the codec parameters.

One of the first things I tried was heading to the MDN sample page and copying the codecs they used there: 'video/mp4; codecs="avc1.42E01E, mp4a.40.2"'. This gave the same "operation not permitted" error. Digging into the meaning of these codec parameters (like what the heck does 42E01E even mean?). While I wish I had a better answer, while Googling it I stumbled upon this StackOverflow post which mentioned using 'video/mp4; codecs="avc1.64000d,mp4a.40.2"' on Safari. I gave it a try and the console errors were gone!

Although the console errors are gone now, I'm still not seeing any video. So there is still work to do.

Update 2

Further investigation in the Debugger in Safari (placing multiple breakpoints and inspecting variables at each step of the process) found that handleDataAvailable was never being called in Safari. It looks like in Firefox and Chrome mediaRecorder.start(100) will properly follow the spec and call ondatavailable every 100 milliseconds, but Safari ignores the parameter and buffers everything into one massive Blob. Calling mediaRecorder.stop() manually caused ondataavailable to be called with everything that had been recorded up until that point

I tried using setInterval to call mediaRecorder.requestData() every 100 milliseconds, but requestData was not defined in Safari (much like how isTypeSupported was not defined). This put me in a bit of a bind.

Next I tried cleaning up the whole MediaRecorder object and creating a new one every 100 milliseconds, but this threw an error on the line await bufferedBlob.arrayBuffer(). I'm still investigating why that one failed

Update 3

One thing I recall about the MP4 format is that the "moov" atom is required in order to play back any content. This is why you can't download the middle half of an MP4 file and play it. You need to download the WHOLE file. So I wondered if the fact that I selected MP4 was the reason I was not getting regular updates.

I tried changing video/mp4 to a few different values and got varying results:

• video/webm -- Operation is not supported
• video/x-m4v -- Behaved like MP4, I only got data when .stop() was called
• video/3gpp -- Behaved like MP4
• video/flv -- Operation is not supported
• video/mpeg -- Behaved like MP4

Everything behaving like MP4 led me to inspect the data that was actually being passed to handleDataAvailable. That's when I noticed this:

No matter what I selected for the video format, Safari was always giving me an MP4!

Suddenly I remembered why Safari was such a nightmare, and why I had mentally classified it as "damned-near impossible". In order to stitch together several MP4s would require a JavaScript transmuxer

That's when I remembered, that's exactly what I had done before. I worked with MediaRecorder and SourceBuffer just over a year ago to try and create a JavaScript RTMP player. Once the player was done, I wanted to add support for DVR (seeking back to parts of the video that had already been streamed), which I did by using MediaRecorder and keeping a ring buffer in memory of 1-second video blobs. On Safari I ran these video blobs through the transmuxer I had coded to convert them from MP4 to ISO-BMFF so I could concatenate them together.

I wish I could share the code with you, but it's all owned by my old employer - so at this point the solution has been lost to me. I know that someone went through the trouble of compiling FFMPEG to JavaScript using emscripten, so you may be able to take advantage of that.

Answer 2

Additionally, I suffered issues with MediaRecorder. At the time of Audio Record, Mime Types are different like

Mac chrome - Mime Type:audio/webm;codecs=opus
Mac Safari - Mime Type:audio/mp4
Windows/Android - Mime Type:audio/webm;codecs=opus
Iphone Chrome - Mime Type:audio/mp4

In PC, I was saving the file as M4a but Audio was not running in IOS. After some analysis and Testing. I decided to convert the file after Upload in Server and used ffmpeg and It worked like a charm.

    <!-- https://mvnrepository.com/artifact/org.bytedeco/ffmpeg-platform -->
    <dependency>
        <groupId>org.bytedeco</groupId>
        <artifactId>ffmpeg-platform</artifactId>
        <version>4.3.2-1.5.5</version>
    </dependency>


 /**
 * Convert the file into MP4 using H264 Codac in order to make it work in IOS Mobile Device
 * @param file
 * @param outputFile
 */
private void convertToM4A(File file, File outputFile) {
    try {
        String ffmpeg = Loader.load(org.bytedeco.ffmpeg.ffmpeg.class);
        ProcessBuilder pb = new ProcessBuilder(ffmpeg, "-i", file.getPath(), "-vcodec", "h264", outputFile.getPath());
        pb.inheritIO().start().waitFor();
    }catch (Exception e ){
        e.printStackTrace();
    }
}