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• Audio/Video de-synchronisation when playing a video on Chrome

  30 novembre 2020, par Sonia Seddiki

  I've been recently working on a project where I try to play a "custom-made" video on an HTML5 player. By custom-made, I mean I concatenate a bunch of videos together using FFmpeg concat demuxer, each of them having the same properties (FPS, bitrate, resolution, timebase, etc).

  


  Now, I'm having a few issues regarding audio/video synchronisation, with a twist : it does not happen on every video player. The video is perfectly synchronised when read on Firefox, but not on Chrome. It is synchronised when read on a "local" video player like VLC.

  


  I assume it has to do with how the video data is presented to the player. I read a little about PTS, DTS, I-P-B frames and I guess the final output may be a little messed up ? But I don't really have a strong lead to follow here.

  


  I tried to find info on how the HTML5 player was implemented by both browsers, but couldn't find much (again, I'm probably not googling this right). Does anyone here know a bit more about the technical aspect of how a video is actually played in a browser ? Or any clue as to why this de-synchronisation doesn't happen on every platform ?

  


  Thank you so much for your help !

  


• Unexpected Exception when using ffmpeg.wasm in Chrome extension

  18 novembre 2020, par Javierd98

  I'm trying to implement a chrome extension which allows me to play flv videos by transcoding them to mp4 and then inserting a video player as it's done on the transcode example from ffmpeg.wasm.

  


  As chrome extensions don't support the execution of downloaded code, I need to use a downloaded version of ffmpeg-core.
I've downloaded the 0.8.4 version and included the folder on the manifest under web_accessible_resources, so that on the javascript file for trancoding the code is :

  


  const { createFFmpeg, fetchFile } = FFmpeg;
const ffmpeg = createFFmpeg({
  log: true,
  corePath: chrome.runtime.getURL('ffmpeg-core/ffmpeg-core.js'),
});

const transcode = async (file) => {
  const { name } = file;
  console.log('Loading ffmpeg-core.js. Transcode URL.');
  await ffmpeg.load();
  console.log('ffmpeg-core loaded.');

  let blob = await fetch(file).then(r => r.blob());
  console.log('blob downloaded');

  ffmpeg.FS('writeFile', name, blob);
  console.log('Start transcoding');
  await ffmpeg.run('-i', name,  'output.mp4');
  console.log('Complete transcoding');
  const data = ffmpeg.FS('readFile', 'output.mp4');

  const video = document.getElementById('output-video');
  video.src = URL.createObjectURL(new Blob([data.buffer], { type: 'video/mp4' }));
}


  


  Once the transcode function is executed, I get the following exception :

  


  ffmpeg.min.js:1 Uncaught (in promise) TypeError: t is not a function
    at ffmpeg.min.js:1
    at f (ffmpeg.min.js:1)
    at Generator._invoke (ffmpeg.min.js:1)
    at Generator.next (ffmpeg.min.js:1)
    at i (ffmpeg.min.js:1)
    at c (ffmpeg.min.js:1)


  


  

  


  Does somebody have any idea of why could this be happening ?

  


  Thanks a lot !

  


• v4l2loopback device detected by Chrome, not seen by Zoom or Firefox

  14 novembre 2020, par uri sh.

  I am trying to create a loopback device from my webcam to be accessible from both Zoom and a browser. I created three v4l2loopback devices :

  


  sudo modprobe v4l2loopback devices=3 video_nr=10,11,12 card_label="Loopback_1","Loopback_2","Virtual_cam" exclusive_caps=1,1,0


  


  followed by :

  


  ffmpeg -i /dev/video0 -f v4l2 -vcodec rawvideo -pix_fmt yuv420p /dev/video10 -f v4l2 /dev/video11


  


  Both devices are detected by Chrome, yet not seen by either Zoom nor Firefox.
Following advice on other questions on stackoverflow I tried setting the device properties using v4l2loopback-ctl, using v4l2loopback-ctl set-caps "video/x-raw,format=UYVY,width=640,height=480" /dev/video10, and got in response :

  


  


  Setting pipeline to PAUSED ...
ERROR : Pipeline doesn't want to pause.
ERROR : from element /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0 : Device '/dev/video10' is not a output device.
Additional debug info :
v4l2_calls.c(636) : gst_v4l2_open () : /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0 :
Capabilities : 0x85208000
Setting pipeline to NULL ...
Freeing pipeline ...
output to /dev/video10 failed

  


  


  I also tried using gst-launch-1.0 :

  


  gst-launch-1.0 v4l2src device=/dev/video0 ! v4l2sink device=/dev/video10


  


  which tells me that /dev/video10 is not an output device :

  


  


  Setting pipeline to PAUSED ...
ERROR : Pipeline doesn't want to pause.
ERROR : from element /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0 : Device '/dev/video10' is not a output device.
Additional debug info :
v4l2_calls.c(636) : gst_v4l2_open () : /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0 :
Capabilities : 0x85208000
Setting pipeline to NULL ...
Freeing pipeline ...

  


  


  I am running Xubuntu 20.04, kernel version 5.4.0-52-generic, with v4l2loopback-dkms v.0.12.3-1ubuntu0.1, and v4l2loopback-utils.

  


  My goal here is to get a device to be consumed by a desktop Node.js server which will open up a web app using xdg-open (thus the need for both Chrome AND Firefox), which will output a processed videostream that could be consumed by a video chat app, such as Zoom or Jitsi.

  


  Any help will be greatly appreciated.