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• build : Add -D_XOPEN_SOURCE=600 to CPPFLAGS on Cygwin

  9 décembre 2016, par Diego Biurrun

  build : Add -D_XOPEN_SOURCE=600 to CPPFLAGS on Cygwin
  This is required to make certain math defines visible on modern Cygwin.
  

  • [DBH] configure

• FFmpeg using avcodec_decode_audio4 to decode an audio frame failed

  14 octobre 2014, par Jeff Chen

  well,I’m learning FFmpeg APIs recently.And I want to get a *.MP4 file’s audio frames but failed. My coding is :

  int pktSize = packet->size;  
  
  while (pktSize > 0) {  
  
      avcodec_get_frame_defaults(self.av_Context->pAudioFrame);  
  
      int gotframe = 0;   
  
      int len = avcodec_decode_audio4(self.av_Context->pAudioCodecCtx, self.av_Context->pAudioFrame, &gotframe, packet);  
  
      if (len < 0) {  
  
          char buffer[1024];  
  
          av_strerror(len, buffer, 1024);  
  
          NSLog(@"decode audio error,error:%d(%s)",len,buffer);  
  
          break;  
  
      }  
  
      if (gotframe) {  
  
          NSLog(@"got a audio frame");  
  
          KxAudioFrame *frame = [self handleAudioFrame:self.av_Context->pAudioFrame];  
  
          if (frame) {  
  
              [self.audioFrames addObject:frame];  
  
              NSLog(@"self.audioFrames.count = %d++",self.audioFrames.count);  
  
          }  
  
      }  
  
      if (len == 0) {  
  
          break;  
  
      }  
  
      pktSize -= len;
  
  }    

  the len always return -22,anyone knows why ?please tell me the answer,thanks very much !

• How do I use ffmpeg to merge all audio streams (in a video file) into one audio channel ?

  16 décembre 2019, par wkimbrough

  I am attempting to use ffmpeg for a number of files.
  The actual number of audio streams (there is usually one channel per stream) per file isn’t known until I’m using ffmpeg.
  The desired outcome is to somehow have ffmpeg get the count of audio channel, use the number in the command line to amerge those into one single audio channel.
  The goal is to create a preview version of the original video file for use in a simple HTML5 page.
  Is this possible in just one call to ffmpeg ?
  (Also, apologies as some parts of this problem I’m still learning about)

  Edit :
  Dumas stackoverflow asker here.
  Yes, I’ve been trying multiple combinations of ffmpeg args.
  To answer the other question, we have video files that have multiple streams, usually with single channels.
  I’ll post some cmdline examples shortly.

  This cmdline example kind of does what I want ; there are 8 streams, and I’m able to combine all audio into one. THe issue is having to know the number before running ffmpeg :

  ffmpeg -i EXAMPLE.MOV -filter_complex "[0:v]scale=-2:720,format=yuv420p[v];[0:a]amerge=inputs=8[a]" -map "[v]" -map "[a]" -c:v libx264 -crf 23 -preset medium -c:a libmp3lame -ar 44100 -ac 2 OUTPUT.mov