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• Envelope pattern in SoX (Sound eXchange) or ffmpeg

  26 mai 2016, par pJay

  I’ve been using SoX to generate white noise. I’m after a way of modulating the volume across the entire track in a way that will create a pattern similar to this :

  White noise envelope effect

  I’ve experimented with fade, but that fades in to 100% volume and fades out to 0% volume, which is just a pain in this instance.

  The tremolo effect isn’t quite what I’m after either, as the frequency of the pattern will be changing over time.

  The only other alternative is to split the white noise file into separate files, apply fade and then apply trim to either end so it doesn’t fade all the way, but this seems like a lot of unnecessary processing.

  I’ve been checking out this example Using SoX to change the volume level of a range of time in an audio file, but I don’t think it’s quite what I’m after.

  I’m using the command-line in Ubuntu with SoX, but I’m open to suggestions with ffmpeg, or any other Linux based command-line solution.

• Android - JavaCV concat videos sound out of sync

  30 mars 2016, par Luis Reja

  Im developing an Android app using Android Studio. The app let you to record 4 videos (steps) from the device camera.

  Once the final step is recorded, the app concat all 4 videos using javacv (with ffmpeg).

  All working fine, I made a procedure to concat the videos, I concat step1 and step 2 to output12, then concat step3 and step4 to output34. Finally I concat output12 and output34. The video looks fine, but the sound is not sync.

  If I reproduce step1,step2,step3,step4,output12 and output34, the sound is sync.

  If I reproduce the final video the sounds is not sync.

  For your information, I reduce the quality video for test purposes.

  Any Clues ? I have been looking for information, but no results.

  This is the procedure to concat videos.

  protected void ConcatTwoVideos(String step1,String step2,String finalvideo){
  
  
  
   FrameGrabber grabber1 = new FFmpegFrameGrabber(Environment.getExternalStorageDirectory() + "/"+step1+".mp4");
  
   try {
  
        grabber1.start();
  
   } catch (FrameGrabber.Exception e) {
  
        e.printStackTrace();
  
   }
  
  
  
   FrameGrabber grabber2 = new FFmpegFrameGrabber(Environment.getExternalStorageDirectory() + "/"+step2+".mp4");
  
   try {
  
        grabber2.start();
  
   } catch (FrameGrabber.Exception e) {
  
        e.printStackTrace();
  
   }
  
  
  
   FrameRecorder recorder2 = new FFmpegFrameRecorder(Environment.getExternalStorageDirectory() + "/"+finalvideo+".mp4", grabber1.getImageWidth(), grabber1.getImageHeight(), grabber1.getAudioChannels());
  
   recorder2.setFrameRate(grabber1.getFrameRate());
  
   recorder2.setSampleFormat(grabber1.getSampleFormat());
  
   recorder2.setSampleRate(grabber1.getSampleRate());
  
   recorder2.setVideoOption("preset", "ultrafast");
  
   recorder2.setVideoCodec(avcodec.AV_CODEC_ID_H264);
  
  
  
  try {
  
      recorder2.start();
  
  } catch (FrameRecorder.Exception e) {
  
      e.printStackTrace();
  
  }
  
  videopaso++;
  
  publishProgress();
  
  Frame frame;
  
  int j = 0;
  
  try {
  
      while ((frame = grabber1.grabFrame()) != null) {
  
          j++;
  
          recorder2.record(frame);
  
  
  
      }
  
  } catch (FrameGrabber.Exception e) {
  
      e.printStackTrace();
  
  } catch (FrameRecorder.Exception e) {
  
      e.printStackTrace();
  
  }
  
  videopaso++;
  
  publishProgress();
  
  try {
  
      while ((frame = grabber2.grabFrame()) != null) {
  
          recorder2.record(frame);
  
  
  
      }
  
  } catch (FrameGrabber.Exception e) {
  
      e.printStackTrace();
  
  } catch (FrameRecorder.Exception e) {
  
      e.printStackTrace();
  
  }
  
  
  
  try {
  
      recorder2.stop();
  
      grabber2.stop();
  
      grabber1.stop();
  
  } catch (FrameRecorder.Exception e) {
  
      e.printStackTrace();
  
  } catch (FrameGrabber.Exception e) {
  
      e.printStackTrace();
  
  }
  
  }

• How to play FFMPEG sound sample with OpenAL ?

  22 mars 2016, par Asim

  I am using FFMPEG to load Audio Video from File. It works with video, but I don’t know how to play audio samples.

  Here is my code to get audio samples :

  m_AdotimeBase = (int64_t(m_Adocdec_ctx->time_base.num) * AV_TIME_BASE) / int64_t(m_Adocdec_ctx->time_base.den);   
  
  if(!m_Adofmt_ctx)
  
  {
  
      //AfxMessageBox(L"m_timeBase");
  
      return FALSE ;
  
  }
  
  int64_t seekAdoTarget = int64_t(m_currFrame) * m_AdotimeBase;   
  
  
  
  
  
  if(av_seek_frame(m_Adofmt_ctx, -1, seekAdoTarget, AVSEEK_FLAG_ANY) < 0)
  
  {
  
      /*CString st;
  
      st.Format(L"%d",m_currFrame);
  
      AfxMessageBox(L"av_seek_frame "+st);*/
  
      m_currFrame = m_totalFrames-1;
  
      return FALSE ;
  
  }
  
  
  
  if ((ret = av_read_frame(m_Adofmt_ctx, &packet)) < 0)
  
          return FALSE;
  
  if (packet.stream_index == 0)       
  
  {
  
      ret = avcodec_decode_audio4(m_Adocdec_ctx, &in_AdeoFrame, &got_frame, &packet);
  
      if (ret < 0) 
  
      {
  
          av_free_packet(&packet);
  
          return FALSE;
  
      }
  
  }

  My problem is I want to listen that sample using OPENAL.

  I would appreciate any tutorials or references on the subject.