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• FFmpeg.wasm demuxing - Get encodedChunks in Javascript

  16 mars 2023, par Kevin Baving

  I am building a video editor whose process looks like this :

  


  Demuxing -> Decoding -> Editing -> Encoding -> Muxing.

  


  The demuxing and muxing process is currently done with mp4box.js. I would like to replace mp4box.js with ffmpeg.wasm. Unfortunately, I can't get along with the process.

  


  What should FFmpeg.wasm do in the demuxing process ?

  


  

  • load a .mp4 file

  


  • extract the encodedVideoChunks and store them as EncodedVideoChunk objects in an array

  


  • extract the encodedAudioChunks and store them as EncodedAudioChunk objects in an array

  


  • get some metadata like : duration, timescale, fps, track_width, track_height, codec, audio_channel_count, sample_rate ....

  


  


  public async loadFile(file: File) {
    let data = await fetchFile(file)
    let blob = new Blob();
    await this.ffmpeg.setProgress(({ratio }) => console.log(`Extracting frames: ${Math.round(ratio * 100)}%`));
    this.ffmpeg.FS('writeFile', 'videoTest.mp4', data);
    //Here is where I am struggling
    //Should look like this: 
    //const command = '-i videoTest.mp4 -c:v copy .... '
    //await this.ffmpeg.run(command);
    //....
}


  


  Lets get deeper into my problem :

  


  Because FFmpeg.wasm is still a cli tool, I have no idea what the best way to safe the encodedChunks into a file is (and what kind of filetype I should use). Further I would like to know how to read that file propertly so that i can safe the input of the file into seperate EncodedVideo- and AudioChunks.

  


• How to make faster screenshots using ffmpeg ?

  18 janvier 2017, par supermario

  I use this command to take screenshots from a video :

   ffmpeg  -i input.mkv -r 0.0033 -vf scale=-1:120 -vcodec png capture-%002d.png

  But usually it takes several minutes even on a powerful machine. I’m wondering if there is a faster way to do so ?

• OpenCV ffmpeg DLL not loaded when running app on Windows 7, works on 8 and 10

  2 novembre 2016, par David G.

  I need to maintain a desktop app written in C++, using Qt and OpenCV for some video processing. As far as I understood, the decoding part of OpenCV is delegated to ffmpeg in a separate DLL for licensing reasons.

  The development environment is on Windows 10, using QT Creator and MSVC12 64-bit as compiler. OpenCV version is 3.0, the official distribution. Here, everything runs fine, I am able to decode a video using VideoCapture::open().

  Issues arise when I try to run the application in a standalone fashion with all the required DLLs in the same folder as the .exe file. All cases below are 64-bit OSes.

  On a Windows 10 computer, not the same as the developement machine and no developer libraries present, the video decoding works fine. I have tested on a Windows 8 machine as well, no issues so far.

  On Windows 7, the things get tricky. The same video files that successfully load during the previous tests are not recognized by the app at all i.e. the isOpened call on VideoCapture returns false. For further testing, I stripped the opencv_ffmpeg300_64.dll file to narrow down the issue on Windows 10 and 8 ; as expected, without this DLL the app is no more able to open the same video files.

  It seems that the DLL is simply not recognized on Windows 7.

  Edit : Further investigation using Process Explorer clearly shows that the aforementioned DLL is not loaded when the app runs on Windows 7.

  • Is there something specific about how Windows 7 manages the DLL path resolution and eventual security measures ? Seems normal that the first search location is the same folder as the executable, which is the case here.

  I have tried to trace using WinApiOverride32, with no results.