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• RGB to YUV422 conversion with ffmpeg, incorrect colors

  22 janvier 2016, par user3578571

  I’m trying to convert an 8bit RGB uncompressed to an mpeg2 mxf file (xdcam 422 HD 1080 50i) which is YUV422. With info from the FFMpeg docs and various websites i made the following command :

  ./ffmpeg -y -i test_lines.mov  -pix_fmt yuv422p -vcodec mpeg2video -non_linear_quant 1 -flags +ildct+ilme -top 1 -dc 10 -intra_vlc 1 -qmax 2 -vtag xd5c -rc_max_vbv_use 1 -rc_min_vbv_use 1 -g 12 -b:v 50000k -minrate 50000k -maxrate 50000k -bufsize 8000k -acodec pcm_s24le -ar 48000 -bf 2 -ac 2 lines_HD.mxf

  This gave me a result with the colors much brighter than the original.

  So i tried adding the options -color_range 1 -colorspace 1 -color_primaries 1 -color_trc 1 but this didn’t seem to do anything.

  After adding colormatrix=bt601:bt709 i got a way better image, but slightly darker than the original and it also feels weird specifying this option cause the source is also in the REC709 colorspace, so why specify it differently ?

  Next i regenerated my source image to an YUV codec (prores) and rerun FFMpeg on it with the colors coming out just fine. Therefore i think it has to be an RGB -> YUV problem.
  Does somebody have an idea how to this properly ? I can provide screenshots of the different results on a videoscope as soon as i’m back at the office, if anybody is interested.

  Last, i know there are various topics touching this subject but either they go way over my head FFmpeg wise or bring me to the stage where i already am.

• Streaming videos from a Java backend

  11 mai 2014, par IAmYourFaja

  I was wondering how most multimedia Java shops handle video streaming. Say I want to build a website that has a page that uses the HTML5 video player like so :

      
  
          ...
  
      
  
      
  
          ... content up here
  
  
  
          <video width="500" height="500" controls="controls" src="path/to/video.mp4"></video>
  
  
  
          ... more content down here

  Say the URL for this page is http://myapp.example.org/video. When HTTP requests for the /video path reach the myappp.example.org servers, I guess I have a few options :

  • Route the request to a web app server (Tomcat/Jetty), and try to figure out how to stream the video.mp4 video directly off that server using pure Java ; or
  • Route the request to a media server, and somehow stream video.mp4 from that media server directly back to the client ; or
    • On this end I’ve heard of servers like Red5 or Wowza
  • Route the request to a media server (again, Red5/Wowza), and somehow stream video.mp4 through the web app server acting as a middleman

  There may be other options that I’m aware of (in which case, what are they ???). My questtion :

  How is A/V streaming typically handled from behind a Java backend ?

• why type casting on non-pointer struct give syntax error

  31 mars 2016, par Sany Liew

  I am using Visual C++ express 2008 try to compile code similar to below :

  no problem

  {
  
    ...
  
    AVRational test = {1, 1000};
  
    ...
  
  }

  but has problem when it is as below :

  {
  
    ...
  
    AVRational test = (AVRational){1, 1000};
  
    ...
  
  }

  gave errors :

  1>..\..\..\projects\test\xyz.cpp(1139) : error C2059: syntax error : '{'
  
  1>..\..\..\projects\test\xyz.cpp(1139) : error C2143: syntax error : missing   ';' before '{'
  
  1>..\..\..\projects\test\xyz.cpp(1139) : error C2143: syntax error : missing ';' before '}'

  where AVRational (ffmpeg.org library) is defined as :

  typedef struct AVRational{
  
      int num; ///< numerator
  
      int den; ///< denominator
  
  } AVRational;

  FFmpeg come with some pre-define value such as

  #define AV_TIME_BASE_Q (AVRational){1, AV_TIME_BASE}

  which is used as below

  av_rescale_q(seek_target, AV_TIME_BASE_Q, pFormatCtx->streams[stream_index]->time_base);

  will failed to compile on Visual C++ express 2008

  It seem like the same code will be compiled with no error/warning on gcc compiler. Why I get this error on VC++ ? Is it a C/C++ standard way to do casting on struct value ? Anyway I can avoid this error while still able to use the defined AV_TIME_BASE_Q ?