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• FFmpeg check channels of a 7.1 audio for silence

  24 septembre 2019, par Tina J

  This is a follow-up question from my previous question asked here, where I needed to look for silence within a specific audio track. Here is the ffmpeg life-saver solution where helps to get some metadata :

  ffmpeg -i file -map 0:a:1 -af astats -f null -

  But I have other type of input .mp4 files where they have one single track of 8 (i.e. 7.1) audio channels. Apparently these files are transcoded from an original file (somehow the 4 track stereos are squished into these files). Now similar to my previous, I need to know if the original file was 2-channel stereo or 5.1 (6) channel.

  How to know if a specific channel of an audio track (say Center channel) is silent/mute, possibly using ffmpeg ? Here is a sample .mp4 file.

• ios Crash when convert yuvj420p to CVPixelBufferRef use ffmpeg

  20 mars 2020, par jansma

  I need to get rtsp steam from ip camera and convert the AVFrame data to CVPixelBufferRef
  in order to send the data to other sdk

  First I use avcodec_decode_video2 to decode video data

  After decode the video I convert the data to CVPixelBufferRef this is my code

  size_t srcPlaneSize = pVideoFrame_->linesize[1]*pVideoFrame_->height;
  
  size_t dstPlaneSize = srcPlaneSize *2;
  
  uint8_t *dstPlane = malloc(dstPlaneSize);
  
  void *planeBaseAddress[2] = { pVideoFrame_->data[0], dstPlane };
  
  
  
  // This loop is very naive and assumes that the line sizes are the same.
  
  // It also copies padding bytes.
  
  assert(pVideoFrame_->linesize[1] == pVideoFrame_->linesize[2]);
  
  for(size_t i = 0; i/ These might be the wrong way round.
  
      dstPlane[2*i  ]=pVideoFrame_->data[2][i];
  
      dstPlane[2*i+1]=pVideoFrame_->data[1][i];
  
  }
  
  
  
  // This assumes the width and height are even (it's 420 after all).
  
  assert(!pVideoFrame_->width%2 && !pVideoFrame_->height%2);
  
  size_t planeWidth[2] = {pVideoFrame_->width, pVideoFrame_->width/2};
  
  size_t planeHeight[2] = {pVideoFrame_->height, pVideoFrame_->height/2};
  
  // I'm not sure where you'd get this.
  
  size_t planeBytesPerRow[2] = {pVideoFrame_->linesize[0], pVideoFrame_->linesize[1]*2};
  
  int ret = CVPixelBufferCreateWithPlanarBytes(
  
          NULL,
  
          pVideoFrame_->width,
  
          pVideoFrame_->height,
  
          kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange,
  
          NULL,
  
          0,
  
          2,
  
          planeBaseAddress,
  
          planeWidth,
  
          planeHeight,
  
          planeBytesPerRow,
  
          NULL,
  
          NULL,
  
          NULL,
  
          &pixelBuf);

  After I run the app the application will crash on

  dstPlane[2*i  ]=pVideoFrame_->data[2][i];

  How to resove this question ?

  this is console in xcode

  All info found
  
  Setting avg frame rate based on r frame rate
  
  stream 0: start_time: 0.080 duration: -102481911520608.625
  
  format: start_time: 0.080 duration: -9223372036854.775 bitrate=0 kb/s
  
  nal_unit_type: 0, nal_ref_idc: 0
  
  nal_unit_type: 7, nal_ref_idc: 3
  
  nal_unit_type: 0, nal_ref_idc: 0
  
  nal_unit_type: 8, nal_ref_idc: 3
  
  Ignoring NAL type 0 in extradata
  
  Ignoring NAL type 0 in extradata
  
  nal_unit_type: 7, nal_ref_idc: 3
  
  nal_unit_type: 8, nal_ref_idc: 3
  
  nal_unit_type: 6, nal_ref_idc: 0
  
  nal_unit_type: 5, nal_ref_idc: 3
  
  unknown SEI type 229
  
  Reinit context to 800x608, pix_fmt: yuvj420p
  
  (lldb) 

  

• How to stitch(concat) two transport stream with two different resolution and I-frame slices format without loosing resolution and slices information

  2 octobre 2019, par AnkurTank

  I have been trying to test a use case with steam captured from multimedia device and that didn’t work. And then I have been trying to create this specific transport stream for like two days now without success, so requesting some help.

  I need to create transport stream with two different resolution and two different slicing format.

  I divided the task in following steps and in last two steps I need help.

  Step 1 : Download sample video with resolution : 1920x1080.
  I downloaded big buck bunny mp4 .

  Step 2 : Create transport stream with following
  resolution : 1920x720, H264 I frame slices per frame : 1
  I used following ffmpeg commands to do that.

  #Rename file to input.mp4
  
  $ mv bbb_sunflower_1080p_30fps_normal.mp4 input.mp4
  
  #Extract transport stream
  
  $ ffmpeg -i input.mp4 -c copy first.ts

  first.ts is having 1980x720 resolution and one H264 I slice per frame.

  Step 3 : Create another transport stream with smaller resolution using following commands

  #Get mp4 with lower resolution.
  
  $ ffmpeg -i input.mp4 -s 640x480 temp.mp4
  
  #Extract trans port stream from mp4
  
  $ ffmpeg -i temp.mp4 -c copy low_r.ts

  Step 4 : Edit(and re-encode ?) low_r.ts to have two H264 I frame slices.
  I used following command to achieve it.

  $ x264 --slices 4 low_r.ts -o second.ts

  However when I play this second.ts on vlc using following command it doesn’t play

  $ vlc ./second.ts 

  And using Elacard StreamEye software when I analyze the transport stream I see that it has 4 H264 I slices in only two times other than that lot of H264 p slices and H264 B slices.
  Need help here to figure out why second.ts doesn’t play and why slicing is not correct.

  Step 5 : Combine both the transport stream without loosing resolution and slicing information.
  Don’t know command for this. Need help here.
  I tried ffmpeg but that combines two stream with different resolution and makes one file with one resolution.

  Any suggestions/pointers would help me proceed. Let me also know if any of the above steps are not fine too.