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• avformat/matroskadec : Don't discard valid packets

  25 mars 2020, par Andreas Rheinhardt

  avformat/matroskadec : Don't discard valid packets
  A Block (meaning both a Block in a BlockGroup as well as a SimpleBlock)
  
  must have at least three bytes after the field containing the encoded
  
  TrackNumber. So if there are <= 3 bytes, the Matroska demuxer would
  
  skip this block, believing it to be an empty, but valid Block.
  This might discard valid nonempty Blocks, namely if the track uses header
  
  stripping. And certain definitely spec-incompliant Blocks don't raise
  
  errors : Those with two or less bytes left after the encoded TrackNumber
  
  and those with three bytes left, but with flags indicating that the Block
  
  uses lacing as then there has to be further data describing the lacing.
  Furthermore, zero-sized packets were still possible because only the
  
  size of the last entry of a lace was checked.
  This commit fixes this. All spec-compliant Blocks that contain data
  
  (even if side data only) are now returned to the caller ; spec-compliant
  
  Blocks that don't contain anything are not returned.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskadec.c

• Extract frames as images from an RTMP stream in real-time

  7 novembre 2014, par SoftForge

  I am streaming short videos (4 or 5 seconds) encoded in H264 at 15 fps in VGA quality from different clients to a server using RTMP which produced an FLV file. I need to analyse the frames from the video as images as soon as possible so I need the frames to be written as PNG images as they are received.

  Currently I use Wowza to receive the streams and I have tried using the transcoder API to access the individual frames and write them to PNGs. This partially works but there is about a second delay before the transcoder starts processing and when the stream ends Wowza flushes its buffers causing the last second not to get transcoded meaning I can lose the last 25% of the video frames. I have tried to find a workaround but Wowza say that it is not possible to prevent the buffer getting flushed. It is also not the ideal solution because there is a 1 second delay before I start getting frames and I have to re-encode the video when using the transcoder which is computationally expensive and unnecessarily for my needs.

  I have also tried piping a video in real-time to FFmpeg and getting it to produce the PNG images but unfortunately it waits until it receives the entire video before producing the PNG frames.

  How can I extract all of the frames from the stream as close to real-time as possible ? I don’t mind what language or technology is used as long as it can run on a Linux server. I would be happy to use FFmpeg if I can find a way to get it to write the images while it is still receiving the video or even Wowza if I can find a way not to lose frames and not to re-encode.

  Thanks for any help or suggestions.

• bash Shell : lost first element data partially

  10 mars 2016, par Sandeep Singh Rana

  Using bash shell :
  I am trying to read a file line by line.
  and every line contains two meaning full file names delimited by "``"

  file:1 image_config.txt

  bbbbb.mp4``thumb/hashdata.gif
  
  bbbbb.mp4``thumb/hashdata2.gif

  Shell Script

  #!/bin/bash
  
  filename="image_config.txt"
  
  
  
  while IFS='' read -r line || [[ -n "$line" ]]; do
  
  
  
  IFS='``' read -r -a array <<< "$line"
  
  if [ "$line" = "" ]; then
  
  echo lineempty
  
  else
  
  
  
  file=${array[0]}
  
  hash=${array[2]}
  
  
  
      echo $file$hash;
  
      output=$(ffmpeg -v warning -ss 2 -t 0.8 -i $file -vf scale=200:-1 -gifflags +transdiff -y $hash);
  
      echo $output;
  
  #    echo ${array[0]}${array[1]}${array[2]}
  
  fi;
  
  
  
  done < "$filename"

  first time executed successfully but when loop executes second time.
  variable file lost bbbbb from bbbbb.mp4
  and following output comes out

  Output :

  user@domain [~/public_html/Videos]$ sh imager.sh 
  
  bbbbb.mp4thumb/hashdata.gif
  
  
  
  .mp4thumb/hashdata2.gif
  
  .mp4: No such file or directory
  
  
  
  lineempty