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• Multiframe Dicom file not readable by some viewers

  12 mai 2023, par PizzaPasNette

  I have developed a program in C++ that works in 2 major steps :

  


  


  • extract frames from a video with ffmpeg and convert them to jpeg
ffmpeg -i videofile.mp4 -q:v 1 -r desired_framerate tmp_04%d.jpeg

    


  


  • create a multiframe Dicom file from those jpeg images via DCMTK

    


    //Example for one image&#xA;&#xA;// Get the n-th image&#xA;QFile* imageFile = new QFile("Path/To/Image");&#xA;&#xA;// Read the image inside a byte array&#xA;QByteArray * ba = new QByteArray();&#xA;imageFile->open(QIODevice::ReadOnly);&#xA;*ba = imageFile->readAll();&#xA;&#xA;// Insert the byte array in the Dicom file&#xA;cond = jpegPixelItem->putUint8Array(reinterpret_cast<uint8>(ba->data()), ba->size());&#xA;&#xA;// Rinse and repeat&#xA;</uint8>

    


  


  


  It works well and can be displayed on most viewers but some complain about the Transfer Syntax being wrong.
As of now, I'm using the "JPEGLossless:Non-hierarchical-1stOrderPrediction" but It seems some viewers can't read my Dicom file unless I change the Transfer Syntax to "JPEG Baseline (Process 1)" which is a lossy Transfer Syntax.

  


  I assume the problem comes from the first step of the program with ffmpeg that might be creating lossy JPEG images but I'm not sure because I'm using the "best" q:v scale as I've seen in other posts on the subject.

  


  Therefore, my 2 main questions are :

  


  

  • why do some viewers have no problems displaying the dicom file whereas some others can't ?

  


  • is there any way to obtain lossless JPEG images from a ffmpeg command ?

  


  


• ffmpeg live stream overlay issues,while any one of the stream is lost other streams are getting stuck

  29 mars 2013, par Samy

  So far we have done

  We have a video chat client which has a set of 9 video streams (users) with
  h.264 codec using Adobe FMS. Now, using ffmpeg we are able to combine these
  streams into one stream using the overlay (video) and amix (audio) filters.
  We are able to send the single combined stream to a live streaming service.
  The stream of the active speaker is shown in a bigger size using the scale
  property of ffmpeg.

  Code as follows :

  ffmpeg -i "rtmp://localhost/live/mystream" -i "rtmp://localhost/live/mystream2 " -i "rtmp://localhost/live/mystream3 "-filter_complex"nullsrc=size=300x300 [b1];[0:v] setpts=PTS-STARTPTS,scale=100x100 [s1];[1:v] setpts=PTS-STARTPTS,scale=200x200 [s2];[2:v]setpts=PTS-STARTPTS,scale=100x100 [s3];[b1][s1] overlay=shortest=1 [b1+s1];[b1+s1][s2] overlay=shortest=1 [b1+s2];
  
  [b1+s2][s3] overlay=shortest=1:x=100" out.mp4

  Help Needed in the following 2 major issues. Any help would be appreciated.

  1. Whenever the active speaker changes, the stream of that user should be shown in a bigger
     size. is this possible to do without restarting the ffmpeg process ?

  2. Right now, if one of the 9 streams stops, the ffmpeg process crashes.

• avcodec/ac3_parser : add avpriv_ac3_parse_header2() and use it in libavcodec

  1er mars 2014, par Michael Niedermayer

  avcodec/ac3_parser : add avpriv_ac3_parse_header2() and use it in libavcodec
  The new function has the ability to allocate the structure, allowing it to grow
  
  without needing major bumps
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/ac3_parser.c
  • [DH] libavcodec/ac3_parser.h
  • [DH] libavcodec/ac3dec.c