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• Why codecs x264/x265 ignores pts and dts of input frame ?

  1er mars 2018, par Iceman

  I’m trying to encode images from a webcam with libx265 (libx264 tried earlier) ...
  The webcam can not shoot with stable FPS because of the different amount of light entering the matrix and, as a result, different delays. Therefore, I count the fps and dts of the incoming frame and set these values for the corresponding parameters of the x265_image object, and init the encoder fpsNum with 1000 and fpsDenom with 1 (for millisecond timebase).
  The problem is that the encoder ignores pts and dts of input image and encodes at 1000 fps ! The same trick with timebase produces smooth record with libvpx. Why it does not work with x264/x265 codecs ?

  Here is parameters initialization :

  ...
  
      error = (x265_param_default_preset(param, "fast", "zerolatency") != 0);
  
      if(!error){
  
          param->sourceWidth = width;
  
          param->sourceHeight = height;
  
          param->frameNumThreads = 1;
  
          param->fpsNum = 1000;
  
          param->fpsDenom =  1;
  
          // Intra refres:
  
          param->keyframeMax = 15;
  
          param->intraRefine = 1;
  
          // Rate control:
  
          param->rc.rateControlMode = X265_RC_CQP;
  
          param->rc.rfConstant = 12;
  
          param->rc.rfConstantMax = 48;
  
          // For streaming:
  
          param->bRepeatHeaders = 1;
  
          param->bAnnexB = 1;
  
          encoder = x265_encoder_open(param);
  
          ...
  
      }
  
  ...

  Here is frame adding function :

  bool hevc::Push(unsigned char *data){
  
      if(!error){
  
          std::lock_guard lock(m_framestack);
  
          if( timer > 0){
  
              framestack.back()->dts = clock() - timer;
  
              timer+= framestack.back()->dts;
  
          }
  
          else{timer = clock();}
  
          x265_picture *picture = x265_picture_alloc();
  
          if( picture){
  
              x265_picture_init(param, picture);
  
              picture->height = param->sourceHeight;
  
              picture->stride[0] = param->sourceWidth;
  
              picture->stride[1] = picture->stride[2] = picture->stride[0] / 2;
  
              picture->planes[0] = new char[  luma_size];
  
              picture->planes[1] = new char[chroma_size];
  
              picture->planes[2] = new char[chroma_size];
  
  
  
              colorspaces::BGRtoI420(param->sourceWidth, param->sourceHeight, data, (byte*)picture->planes[0], (byte*)picture->planes[1], (byte*)picture->planes[2]);
  
              picture->pts = picture->dts = 0;
  
              framestack.emplace_back(picture);
  
          }
  
          else{error = true;}
  
      }
  
      return !error;
  
  }

  Global PTS is increasing right after x265_encoder_encode call :
  pts+= pic_in->dts; and sets as a pts of new image from framestack queue when it comes to encoder.

  Can the x265/x264 codecs encode at variable fps ? How to configure it if yes ?

• Multimedia Exploration Journal : The Past Doesn’t Die

  12 juillet 2011, par Multimedia Mike — Game Hacking

  New haul of games, new (old) multimedia formats.

  Lords of Midnight
  Check out the box copy scan for Lords of Midnight in MobyGames. In particular, I’d like to call your attention to this little blurb :

  
  
  

  Ahem, "Journey through an immense world — the equivalent of 8 CD-ROMs." Yet, when I procured the game, it only came on a single CD-ROM. It’s definitely a CD-ROM (says so on the disc) and, coming from 1995, certainly predates the earliest DVD-ROMs (which can easily store 8 CD-ROMs on a disc). Thus, I wanted to jump in a see if they were using some phenomenal compression in order to squeeze so much info into 600 or so megabytes.

  I was surprised to see the contents of the disc clocking in at just under 40 megabytes. An intro movie and an outro movie account for 75% of that. Format ? None other than that curious ASCII anomaly, ARMovie/RPL with Escape 122 codec data.

  Cyclemania

  
  
  

  Cyclemania is one of those FMV backdrop action games, but with a motorcycle theme. I had a good feeling I would find some odd multimedia artifacts here and the game didn’t disappoint. The videos are apparently handled using 3-4 discrete files per animation. I’ve documented my cursory guesses and linked some samples at the new MultimediaWiki page.

  Interplay ACMP
  This is unrelated to this particular acquistion, but I was contacted today about audio files harvested from the 1993 DOS game Star Trek : Judgment Rites. The files begin with the ASCII signature "Interplay ACMP Data". This reminds me of Interplay MVE files which begin with the similar string "Interplay MVE File". My theory is that these files use the ACOMP compression format, though I’m still trying to make it fit.

  Wiki and samples are available as usual if you’d like to add your own research.

• Convert mp3 to AAC with mpeg-2 container (FFMPEG)

  18 mars 2016, par jsurf

  I’m trying to convert an mp3 audio file to an AAC file with FFMPEG, and I need the audio to be wrapped in an MPEG-2 container.
  The resulting AAC file needs to be AAC-LC (Low Complexity), 1-channel, CBR mode, 44100 sample rate, and 48kb/s bitrate, so I use this command :

  ffmpeg -y -i input.mp3 -ar 44100 -ab 48k -acodec libfdk_aac -ac 1 output.aac

  But when I examine the ADTS headers, the audio file is always being wrapped in an MPEG-4 container. I have tried all the codecs listed here but I still end up with an mpeg-4 container wrapped around the audio : http://trac.ffmpeg.org/wiki/AACEncodingGuide.

  Here are the headers I get when examining the AAC output file :

  mpeg_type : ’MPEG4’,
  profile : 2,
  profile_name : ’AAC LC’,
  sample_freq : 44100,
  channel_config : 1,
  channels : 1,
  frame_length : 139,
  buffer_fullness : 157,
  number_of_frames : 1,
  frames_per_sec : 43.06640625

  Any ideas as to why ffmpeg wraps an mp4 container around the audio ? Can I get around this somehow ? Are there any other encoders I can try aside from FFMPEG ? I was giving FAAC encoder a shot and it gives me the proper encoding and ADTS headers, but alas it does not support mp3, only WAV.