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• How to synchronize audio and video using ffmpeg libraries ?

  21 octobre 2013, par jsp99

  Stuck writing a very basic media player in C, using SDL and ffmpeg libraries. Initially, followed the theory in this page to get an idea about the entire program and the usage of libraries. After coding from scratch, thanks to that tutorial and many other resources, finally I made my code work, using the latest libraries of ffmpeg and SDL (2.0). But my code lacks a proper synchronization mechanism (actually it lacks a sync mechanism !).

  I still don't have a clear idea on how to synchronize the audio and video together as the theory provided in the link is only very partially correct (atleast when it comes to using the latest dev libraries).
  For example, a sentence in this page is as follows :

  However, ffmpeg reorders the packets so that the DTS of the packet being processed by avcodec_decode_video() will always be the same as the PTS of the frame it returns.

  I am using avcodec_decode_video2() and the DTS of the packet is definitely not the same as pts of the frame it decodes (in general).

  I read this very informative BBC report and it makes complete sense. I have a clear idea about PTS and DTS. But the PTS and DTS values that ffmpeg is using for packets and decoded frames is confusing. I wish there were some documentation on that aspect.

  Can someone explain the steps to synchronize audio and video ? I only need the steps. I am quite comfortable implementing them. Any help is greatly appreciated. Thanks !

  PS : Here's a screenshot of what I am talking about :

  

  The huge negative value is, I assume AV_NOPTS_VALUE.

• Merge commit ’05a4bacbf7ece618553d339afe1d0b57bc87aea8’

  9 juillet 2016, par Clément Bœsch

  Merge commit ’05a4bacbf7ece618553d339afe1d0b57bc87aea8’
  * commit ’05a4bacbf7ece618553d339afe1d0b57bc87aea8’ :
  
    avpacket : Error out when creating 0-sized side data
  This commit is a noop, see 5a633ec2dd453c67ff23819c28d98e6b09c47295
  AV_PKT_DATA_METADATA_UPDATE can be zero sized in order to clear old
  
  meta.
  Note : maybe we could add a start or end marker.
  Merged-by : Clément Bœsch <u@pkh.me>
  

• Rendering video by ffmpeg.wasm in browser occured an error

  15 septembre 2022, par James Bor

  When a local video renderer uses the ffmpeg.wasm library in the Chrome browser, very often an error with the SBOX_FATAL_MEMORY_EXCEEDED code occurs during the rendering process. The standard command set is used. The code below is half fake because it is very long, but describes an approximate action algorithm. Computer performance and RAM capacity do not affect the video, files used - minimal size. Has anyone experienced this and how can we solve it ?
Error screen

  


  const videoGenerate = async (project) => {
  const ffmpeg = createFFmpeg({
      corePath: 'ffmpeg/ffmpeg-core.js',
      workerPath: 'ffmpeg/ffmpeg-core.worker.js'
  });
  await loadFfmpeg(ffmpeg);
  project.projectName = "Default";
  project.fileType = "video/mp4";

  const resultVideo = {
    title: `${project.projectName}ConcatenatedVideo.mp4`,
  };
  // *For fetchFile method and ffmpeg.FS('writeFile', title, file);
  await uploadObjects(project.projectName, ffmpeg);
  // *
  const command = ['-i', project.video, resultVideo.title];
  await ffmpeg.run(...command);
  await ffmpeg.FS("unlink", resultVideo.title);
  resultVideo["blob"] = ffmpeg.FS('readFile', title);
  return resultVideo.blob;
};


  


  These dependencies are used : "@ffmpeg/core" : " 0.8.5", "@ffmpeg/ffmpeg" : " 0.9.7". Upgrading the library to the latest version does not work either.