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• avcodec/h2645_sei : loosen up min luminance requirements

  25 mai 2024, par Niklas Haas

  avcodec/h2645_sei : loosen up min luminance requirements
  The H.265 specification is quite clear on this case :
  > When min_display_mastering_luminance is not in the range of 1 to
  
  > 50000, the nominal maximum display luminance of the mastering display
  
  > is unknown or unspecified or specified by other means not specified in
  
  > this Specification.
  And so the current code is correct in marking luminance data as invalid
  
  if min luminance is set to 0. However, this breaks playback of at least
  
  several real-world Blu-ray releases, for example La La Land, Planet of
  
  the Apes, and quite possibly a lot more. These come with ostensibly
  
  valid max_luminance tags (1000 nits), but min_luminance set to 0.
  Loosen up this requirement by guarding it behind FF_COMPLIANCE_STRICT.
  
  We still reject blatantly invalid metadata (wrong value range on
  
  luminance, max set to 0, max below min, min above 50 nits etc.), so this
  
  shouldn't cause any unintended regressions.
  Fixes : https://github.com/mpv-player/mpv/issues/14177
  

  • [DH] libavcodec/h2645_sei.c

• Is there a way to apply a curve bend in ffmpeg ?

  25 mars 2020, par stevendesu

  I have four cameras each feeding me a different portion of a basketball court. Due to the slight offset of the cameras physical locations and lens distortion around the edges of the camera, I cannot simply stitch the videos together without some kind of correction.

  I’ve looked into ffmpeg’s perspective filter, as well as the lenscorrection filter. In the former case it was only able to create a trapezoid, not the curved image I want. In the latter case using negative values to k1 and k2 seemed to be heading in the right direction, but it either disorted the top and bottom of the image to the point of being nonsensical noise, or it zoomed in to the image so much that I lost important details.

  For the sample picture below, ultimately I want the midcourt line (the blue vertical line on the right side) to be vertical, and I want the mess of wires on the white desk at the bottom to remain visible and identifiable.

  Given a video which looks like the following :

  

  I wish to produce something like the following :

  

  This image was made using the "Curve Bend" filter in GIMP, but I just eye-balled it - so it’s not perfect. Ideally once I get the exact parameters the midcourt line will be perfectly vertical

  When using the lenscorrection filter, no values for k1 and k2 seemed to get the effect I want :

  Negative k1, negative k2 :

  

  Negative k1, positive k2 :

  

  Positive k1, negative k2 :

  

  Positive k1, positive k2 :

  

  In general :

  • negative / negative distorted the image beyond recognition
  • negative / positive looked alright, but the midcourt line was off the screen and it wasn’t clear if any distortion had been applied
  • positive / negative looked the best, but while the top and bottom curved in the middle of the left and right actually bulged out, leaving the midcourt line distorted
  • positive / positive was the opposite of the desired effect

• How to save data of packet.data using ffmpeg && c language ?

  12 juin 2015, par patrick

  I’m try to build an app in c that extract audio from video and save it as audio file. I’m able to extract the audio but now the problem is how to save it. I wrote the code given below but it’s giving me an segmentation fault. Thanks in advance.

  My code is :

  AVOutputFormat* fmt = av_guess_format("mp3", NULL, NULL);;
  
  AVFormatContext* oc = avformat_alloc_context();
  
  oc->oformat = fmt;
  
  avio_open2(&oc->pb, "test.mp3", AVIO_FLAG_WRITE,NULL,NULL);
  
  
  
  AVStream* stream=NULL;
  
  int cnt = 0;
  
  
  
  while(av_read_frame(pFormatCtx, &packet)>=0) { //pFormatCtx is input file format context.
  
      if (packet.stream_index==audioStream) {
  
      int got_frame = 0;
  
      if (avcodec_decode_audio4(pCodecCtx, pFrame, &got_frame, &packet) < 0) {
  
          fprintf(stderr, "Error encoding frame\n");
  
                  exit(1);
  
          }
  
  
  
          if(got_frame) {
  
          if (av_interleaved_write_frame(oc, &packet) < 0) {
  
                  printf(stderr, "Error writing frame\n");
  
                      exit(1);
  
                  }
  
          }
  
      }
  
      av_free_packet(&packet);
  
      av_init_packet(&packet);
  
  }