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• FFMPEG merging sounds with amix cause volume problem [duplicate]

  10 mars 2020, par birdcage

  I am trying to combine many sounds with FFMPEG amix command and I need to set the starting moment of every sound. Every sound has different duration.

  When I use the command below, the volume of first and last item seems different in merged file. It seems the level of sound increases till the end of merged sound. I am wondering what I do wrong.

  ffmpeg -i 1.wav -i 2.wav -i 3.wav -i 4.wav -filter_complex 
  
  "[0]adelay=1000|1000[a]; 
  
  [1]adelay=30000|30000[b]; 
  
  [2]adelay=50000|50000[c]; 
  
  [3]adelay=200000|200000[d];  
  
  [a][b][c][d]amix=4" 
  
  /Users/username/Desktop/final.wav

• X264 : How to access NAL units from encoder ?

  18 avril 2014, par user1884325

  When I call

  frame_size = x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);

  and subsequently write each NAL to a file like this :

       if (frame_size >= 0)
  
       {
  
          int i;
  
          int j;
  
  
  
          for (i = 0; i < i_nals; i++)
  
          {
  
             printf("******************* NAL %d (%d bytes) *******************\n", i, nals[i].i_payload);
  
             fwrite(&(nals[i].p_payload[0]), 1, nals[i].i_payload, fid);
  
          }
  
       }

  then I get this

  

  My questions are :

  1) Is it normal that there’s readable parameters in the beginning of the file ?

  2) How do I configure the X264 encoder so that the encoder returns frames that I can send via UDP without the packet getting fragmented (size must be below 1390 or somewhere around that).

  3) With the x264.exe I pass in these options :

  "--threads 1 --profile baseline --level 3.2 --preset ultrafast --bframes 0 --force-cfr --no-mbtree --sync-lookahead 0 --rc-lookahead 0 --keyint 1000 --intra-refresh" 

  How do I map those to the settings in the X264 parameters structure ? (x264_param_t)

  4) I have been told that the x264 static library doesn’t support bitmap input to the encoder and that I have to use libswscale for conversion of the 24bit RGB input bitmap to YUV2. The encoder, supposedly, only takes YUV2 as input ? Is this true ? If so, how do I build libswscale for the x264 static library ?

• 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 ?