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• Decode h264 video bytes into JPEG frames in memory with ffmpeg

  5 février 2024, par John Karkas

  I'm using python and ffmpeg (4.4.2) to generate a h264 video stream from images produced continuously from a process. I am aiming to send this stream over websocket connection and decode it to individual image frames at the receiving end, and emulate a stream by continuously pushing frames to an <img style='max-width: 300px; max-height: 300px' /> tag in my HTML.

  


  However, I cannot read images at the receiving end, after trying combinations of rawvideo input format, image2pipe format, re-encoding the incoming stream with mjpeg and png, etc. So I would be happy to know what the standard way of doing something like this would be.

  


  At the source, I'm piping frames from a while loop into ffmpeg to assemble a h264 encoded video. My command is :

  


          command = [
            'ffmpeg',
            '-f', 'rawvideo',
            '-pix_fmt', 'rgb24',
            '-s', f'{shape[1]}x{shape[0]}',
            '-re',
            '-i', 'pipe:',
            '-vcodec', 'h264',
            '-f', 'rawvideo',
            # '-vsync', 'vfr',
            '-hide_banner',
            '-loglevel', 'error',
            'pipe:'
        ]


  


  At the receiving end of the websocket connection, I can store the images in storage by including :

  


          command = [
            'ffmpeg',
            '-i', '-',  # Read from stdin
            '-c:v', 'mjpeg',
            '-f', 'image2',
            '-hide_banner',
            '-loglevel', 'error',
            f'encoded/img_%d_encoded.jpg'
        ]


  


  in my ffmpeg command.

  


  But, I want to instead extract each individual frame coming in the pipe and load in my application, without saving them in storage. So basically, I want whatever is happening at by the 'encoded/img_%d_encoded.jpg' line in ffmpeg, but allowing me to access each frame in the stdout subprocess pipe of an ffmpeg pipeline at the receiving end, running in its own thread.

  


  

  • What would be the most appropriate ffmpeg command to fulfil a use case like the above ? And how could it be tuned to be faster or have more quality ?

  


  • Would I be able to read from the stdout buffer with process.stdout.read(2560x1440x3) for each frame ?

  


  


  If you feel strongly about referring me to a more update version of ffmpeg, please do so.

  


  PS : It is understandable this may not be the optimal way to create a stream. Nevertheless, I do not find there should be much complexity in this and the latency should be low. I could instead communicate JPEG images via the websocket and view them in my <img style='max-width: 300px; max-height: 300px' /> tag, but I want to save on bandwidth and relay some computational effort at the receiving end.

  


• ffmpeg-next how can I enable multithreading on a decoder ?

  14 décembre 2022, par Brandon Piña

  I'm using the rust crate ffmpeg-next to decode some video into individual frames for usage in another library. Problem is when I run my test it only seems to use a single core. I've tried modifying the threading configuration for my decoder as you can see below, but It doesn't seem to be do anything

  


          let context_decoder =
            ffmpeg_next::codec::context::Context::from_parameters(input_stream.parameters())?;
        let mut decoder = context_decoder.decoder().video()?;
        let mut threading_config = decoder.threading();
        threading_config.count = num_cpus::get();
        threading_config.kind = ThreadingType::Frame;

        decoder.set_threading(threading_config);


  


• Revision 085f76e535 : Add experimental VBR adaptation method. Add code to monitor over and under spen

  15 avril 2014, par Paul Wilkins

  Changed Paths :
   Modify /vp9/encoder/vp9_firstpass.c

  
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Modify /vp9/encoder/vp9_ratectrl.c

  
   Modify /vp9/encoder/vp9_ratectrl.h

  
  
  Add experimental VBR adaptation method.

  Add code to monitor over and under spend and
  apply limited correction to the data rate of subsequent
  frames. To prevent the problem of starvation or overspend
  on individual frames (especially near the end of a clip) the
  maximum adjustment on a single frame is limited to a %
  of its un-modified allocation.

  Change-Id : I6e1ca035ab8afb0c98eac4392115d0752d9cbd7f