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• how to assign the video level to struct AVCodecContext in ffmpeg ?

  14 juin 2019, par Lichard

  I am writting a C++ video encode API with ffmpeg.The video level is one important param, but I don’t known how to assign it to AVCodecContext.

  I read the ffmpeg document and find out that "level" is int type,below is the definition at line 3014 of file avcodec.h.

             /**
  
   3010      * level
  
   3011      * - encoding: Set by user.
  
   3012      * - decoding: Set by libavcodec.
  
   3013      */
  
   3014      int level;
  
   3015 #define FF_LEVEL_UNKNOWN -99

  according to my google search, the value of level is from 1.1(1.2,1.3,2...) to 5.2, obviously it is not an int type. I think level should be an enum type,but I can’t find any definition about it.

  I have see some usage in internet, such as :

    AVCodecContect *pCtx;
  
    pCtx->level = 3;
  
    ....//or 
  
    pCtx->level = 50;

  but I think these usages are wrong..
  I think the correct way to assign is somehow like this :

    pCtx->level = FF_LEVEL_UNKNOWN;

  so I wonder if there is some relevant enum type definition about level and how to location it.

• x264 rate control

  31 août 2012, par Craig

  We are using the x264 encoder in a video conferencing project, we have the basic streaming video working, however, we are having trouble understanding how the various rate control settings determine the final bitrate.
  We set the following params :

  x264_param_t params;
  
  x264_param_default_preset(&params, "ultrafast", "zerolatency");
  
  params.i_threads = 1;
  
  params.i_width = width;
  
  params.i_height = height;
  
  params.i_fps_num = fps;
  
  params.i_keyint_max = fps;
  
  params.b_intra_refresh = 1;
  
  params.b_repeat_headers = 1;
  
  params.b_annexb = 1;
  
  
  
  //Set rate control stuff here
  
  
  
  x264_param_apply_profile(&params, "baseline");

  If we only set the params.rc.i_bitrate param, the encoder seems to massively overshoot the bitrate. If we set the i_vbv_max_bitrate & i_vbv_buffer_size params we see a bitrate which peaks (and sometimes overshoots) the i_vbv_max_bitrate setting. Obviously having tight control over the biterate is important for video conferencing, but the documentation is kind of opaque. Is anybody else using x264 for video conferencing ? How are you setting the encoder ? Any help appreciated, thanks in advance.

• How is video decoding corruption debugged ?

  20 novembre 2013, par TopGunCoder

  I just started working for a new company and my new role demands that I help debug the video corruption that they are receiving through decoding frames. As much as I intend on digging down deep into the code and looking into the specifics of my problem, it made me think about video debugging in general.

  Since handling videos is very new to me, the whole process seems pretty complex and it seems there are a lot of places for corruption to present itself. The way I see it there is at least three places where corruption could pop up (barring memory corruption from the machine) :

  • Transporting the data before it is decoded
  • decoding implementation that perpetuates corruption once it is encountered, or is all together incorrect (Which seems to be my problem)
  • Transportation to the monitor(which seems unlikely but possible)

  So what i'm really curious about is if/how people debug their video streams to determine the location of any potential corruption they are encountering. I'm sure there is no sure fire method but I am curious to see what problems are even possible and how they can be identified and triaged.

  P.S. - I'm not sure of the differences between different decoding methods but, if this question seems too vague maybe it helps to mention I am using ffmpeg and avcodec_decode_video2 for the decoding.