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• How to send encoded video (or audio) data from server to client in a way that's decodable by webcodecs API using minimal latency and data overhead

  11 janvier 2023, par Tiger Yang

  My question (read entire post for context) :

  


  Given the unique circumstance of only ever decoding data from a specifically-configured encoder, what is the best way I can send the encoded bitstream along with the bare minimum extra bytes required to properly configure the decoder on the client's end (including only things that change per stream, and omitting things that don't, such as resolution) ? I'm a sucker for zero compromises, and I think I am willing to design my own minimal container format to accomplish this.

  


  Context and problem :

  


  I'm working on a remote desktop implementation that consists of a server that captures and encodes the display and speakers using FFmpeg and forwards it via pipe to a go (language) program which sends it on two unidirectional webtransport streams to my client, which I plan to decode using the webcodecs API. According to MDN, the video decoder needs to be fed via .configure() an object containing the following : https://developer.mozilla.org/en-US/docs/Web/API/VideoDecoder/configure before it's able to decode anything.

  


  same goes for the audio decoder : https://developer.mozilla.org/en-US/docs/Web/API/AudioDecoder/configure

  


  What I've tried so far :

  


  Because this remote desktop will be for my personal use only, it would only ever receive streams from a specific encoder configured in a specific way encoding video at a specific resolution, framerate, color space, etc.. Therefore, I took my video capture FFmpeg command...

  


  videoString := []string{
        "ffmpeg",
        "-init_hw_device", "d3d11va",
        "-filter_complex", "ddagrab=video_size=1920x1080:framerate=60",
        "-vcodec", "hevc_nvenc",
        "-tune", "ll",
        "-preset", "p7",
        "-spatial_aq", "1",
        "-temporal_aq", "1",
        "-forced-idr", "1",
        "-rc", "cbr",
        "-b:v", "500K",
        "-no-scenecut", "1",
        "-g", "216000",
        "-f", "hevc", "-",
    }


  


  ...and instructed it to write to an mp4 file instead of outputting to pipe, and then I had this webcodecs demo https://w3c.github.io/webcodecs/samples/video-decode-display/ demux it using mp4box.js. Knowing that the demo outputs a proper .configure() object, I blindly copied it and had my client configure using that every time. Sadly, it didn't work, and I since noticed that the "description" part of the configure object changes despite the encoder and parameters being the same.

  


  I knew that mp4 files worked via mp4box, but they can't be streamed with low latency over a network, and additionally, ffmpeg's -f parameters specifies the muxer to use, but there are so many different types.

  


  At this point, I think I'm completely out of my depth, so :

  


  Given the unique circumstance of only ever decoding data from a specifically-configured encoder, what is the best way I can send the encoded bitstream along with the bare minimum extra bytes required to properly configure the decoder on the client's end (including only things that change per stream, and omitting things that don't, such as resolution) ? I'm a sucker for zero compromises, and I think I am willing to design my own minimal container format to accomplish this. (copied above)

  


• Evolution #3958 : Mise à jour de la liste des types mines

  12 juin 2017, par nico d_

  Hop, pour information ce sont les type MIME, pas mines :)
  Type mine c’est pour les voitures ^^
  https://fr.wikipedia.org/wiki/Type_MIME

  Et sinon, ils sont indiqués ici dans le tableau apparemment :
  https://en.wikipedia.org/wiki/High_Efficiency_Image_File_Format#Brands_and_MIME_types

• python 3 using ffmpeg in a subprocess getting stderr decoding error

  4 mai 2024, par jdauthre

  I am running ffmpeg as a subprocess and using the stderr to get various bits of data like the subtitles stream Id's. It works fine for most videos, but one with japanese subtitles results in an error :

  


  'charmap' codec can't decode byte in position xxx : character maps to

  


  Much googling suggests the problem is that the japanese requires unicode, whereas English does not. Solutions offered refer to problems with files, and I cannot find a way of doing the same with the stderr. Relevent Code is below :

  


  command = [ffmpeg,"-y","-i",fileSelected,"-acodec","pcm_s16le",
                  "-vn","-t","3", "-f",            "null","-"]
print(command)   
proc = subprocess.Popen(command,stderr=PIPE,Jstdin=subprocess.PIPE,
                            universal_newlines=True,startupinfo=startupinfo)
  
stream = ""    
for line in proc.stderr:
    try:
        print("line",line)
    except exception as error:
        print("print",error)
        line = line[:-1]
        if "Stream #" in line:
            estream = line.split("#",1)[1]
            estream =estream.split(" (",1)[0]
            print("estream",estream)
            stream = stream + estream +"\n"  #.split("(",1)[0] 
            stream = stream + estream +"\n"