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• Android : How to convert WAV/PCM to another audio format without MediaCodec API

  3 octobre 2013, par khelkun

  I've searched around the web and stackoverflow during a long time about this subject. I know it has been discussed many times but I'm looking for a friendly opinion on my use case.

  I have a vocal dictation application which uses android.media.AudioRecord. It allows me to edit the recorded raw PCM buffer : insert a new record inside it, delete a certain period in the record, append a new record at the end. The result is a WAV file, but it's a bit too big file for my needs, so I want to convert it to smaller file format.

  android.media.MediaCodec could have been the solution, but it requires API level 16 which is a too high restriction in my situation.

  It sounds to me that I only have 2 options :

  1. Use the NDK and an android portage of ffmpeg like the guardian project android-ffmpeg-java. But this solution sounds a bit too hard for me so far.

  2. Recording with android.media.MediaRecorder to output an audio 3GPP file encoded with the AMR_NB encoder. Then I'll have to understand this 3GPP file header and the AMR_NB format in details to be able to perform the audio editing operations on my record.

  I must also add that creating a zip file of the WAV file is not a valid option for me.

  Does someone know another option please ? And is option 2. actually possible to achieve ?

  Thanks for your time !

• Ffmpeg decode H264 video from RTP stream very slow

  3 octobre 2013, par Dmitry Bakhtiyarov

  I have H264 RTP stream over network and I need to decode it. I use libx264 to encode stream and ffmpeg to decode. When I connect to server using VLC, it correct play video without any problem. But when I connect to server using my application I have a long period, when widget, which draw video from this stream, draw only one image.

  I check log file and found, that avcodec_decode_video2() set got_image into 1 very rarely ! Decoder give me new decoded frame average every 1-2 seconds, but on the server I have 12-15 fps on encoder !

  What the reasons of this delays on decoder and how I can fix its ?

  avcodec_register_all();
  
  av_init_packet(&m_packet);
  
  m_decoder = avcodec_find_decoder(CODEC_ID_H264);
  
  if (!m_decoder)
  
  {
  
      QString str = QString("Can't find H264 decoder!");
  
      emit criticalError(str);
  
  }
  
  m_decoderContext = avcodec_alloc_context3(m_decoder);
  
  
  
  m_decoderContext->flags |= CODEC_FLAG_LOW_DELAY;
  
  m_decoderContext->flags2 |= CODEC_FLAG2_CHUNKS;
  
  AVDictionary* dictionary = nullptr;
  
  if (avcodec_open2(m_decoderContext, m_decoder, &dictionary) < 0)
  
  {
  
      QString str = QString("Failed to open decoder!");
  
      emit criticalError(str);
  
  }
  
  qDebug() << "H264 Decoder successfully opened";
  
  m_picture = avcodec_alloc_frame();
  
  ...
  
      while(m_packet.size > 0)
  
      {
  
          int got_picture;
  
          int len = avcodec_decode_video2(m_decoderContext, m_picture, &got_picture, &m_packet);
  
          if (len < 0)
  
          {
  
              QString err("Decoding error");
  
              qDebug() << err;
  
              //emit criticalError(err);
  
              return false;
  
          }
  
          if (got_picture)
  
          {
  
                  //create from frame QImage and send it into GUI thread
  
              qDebug() << "H264Decoder: frame decoded!";

  I try to change some options of m_decoderContext (i.e. thread_count) but this not changing anything.

• Drop late RTMP AVPackets - FFmpeg

  25 novembre 2014, par Mihai Ghete

  I’m using FFmpeg to read RTMP streams in an iOS application. It is basically a Player for RTMP streams. The problem is that when the network is to busy, av_read_frame takes too much time. In conclusion, the latency increases over time. Are there some FFmpeg setups that I can use so that it will drop late frames or make av_read_frame return if it was unable to read the packet in a defined period of time ?

  Any suggestion would be helpful. Thank you in advance.