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• libavcodec/mpeg12dec : append CC data to a53_buf_ref

  14 décembre 2024, par Scott Theisen

  libavcodec/mpeg12dec : append CC data to a53_buf_ref
  In mpeg_decode_a53_cc() only the A/53 part 4 CC data ("GA94") is saved between
  
  frames. The other formats incorrectly created a larger buffer than they use
  
  since a705bcd763e344fac191e157ffeddc285388b7fa because they did not append to
  
  the previous data.
  The a53_buf_ref is added to the frame in mpeg_field_start() which will only be
  
  called in decode_chunks() if not all of the picture data slices are skipped.
  For these formats, utilize the data added to the buffer in case frames are skipped
  
  (concatenating the CC data until a frame can be exported), in a similar fashion to
  
  the A/53 part 4 logic.
  Reviewed-by : Marth64 <marth64@proxyid.net>
  
  Signed-off-by : Marth64 <marth64@proxyid.net>
  

  • [DH] libavcodec/mpeg12dec.c

• avcodec/mpegvideo : Remove pblocks

  28 avril 2024, par Andreas Rheinhardt

  avcodec/mpegvideo : Remove pblocks
  It has been added in a579db0c4fe026d49c71d1ff64a2d1d07c152d68
  
  due to XvMC, but today it is only used to swap U and V
  
  for VCR2, a MPEG-2 variant with U and V swapped.
  
  This can be done in a simpler fashion, namely by simply
  
  swapping the U and V pointers of the corresponding
  
  MPVWorkPictures.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/mpeg12dec.c
  • [DH] libavcodec/mpegvideo.c
  • [DH] libavcodec/mpegvideo.h

• Pipe video frames from ffmpeg to canvas without loading the entire video into memory

  1er janvier 2024, par Aviato

  I am working on a project that involves frame manipulation and I decided to choose node canvas API for that. I used to work with OpenCV Python and there was a cv2.VideoCapture class that takes a video as input and prepares to read the frames of the video and we can loop through the frames one at a time without having to load all the frames at once in memory.
Now I tried a lot of ways to replicate the same using ffmpeg, i.e. trying to load frames from a video in an ordered, but "on-demand," fashion.

  


  I tried using ffmpeg as a child process to process frames and standout the frames.

  


  const spawnProcess = require('child_process').spawn,
    ffmpeg = spawnProcess('ffmpeg', [
        '-i', 'test.mp4',
        '-vcodec', 'png',
        '-f', 'rawvideo',
        '-s', '1920*1080', // size of one frame
        'pipe:1'
    ]);
ffmpeg.stdout.on('data', (data) => {
    try {
        // console.log(tf.node.decodeImage(data).shape)
        console.log(`${++i} frames read`)
        //context.drawImage(data, 0, 0, width, height)
        
        
    } catch(e) {
        console.log(e)
    } 
})


  


  The value in the console shows something around 4000 + console logs, but the video only had 150 frames, after much investigating and console logging the data, I found that was buffer data, and it's not processing it for each frame. The on-data function returns the buffer data in an unstructured way
I want to read frames from a video and process each one at a time in memory, I don't want to hold all the frames at once in memory or in the filesystem.

  


  

  


  I also want to pipe the frames in a format that could be rendered on top of a canvas using drawImage