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• MP3 audio recording from an input device using the FFmpeg API

  25 novembre 2014, par Hascoet Julien

  I’ve been trying to use the ffmpeg library (I’m working in C with the ffmpeg API) to decode and encode in mp3 from my microphone on Linux. The mp3lane lib is installed and I manage to open all codecs and to decode input samples.
  Here are my input settings :

  Input #1, alsa, from 'default':
  
    Duration: N/A, start: 1416946099.454877, bitrate: 1536 kb/s
  
      Stream #1:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s

  And I manage to decode it ; therefore, it gives me 2 channels of 64 samples after calling avcodec_decode_audio4 right after av_read_frame. The output frame that avcodec_decode_audio4 just gave me seems to be ok with 2 channels as well and 64 samples per channel. Packets are size of 256 and 16-bit*2*64 = 256 bytes so that makes sense.

  The problem is when i’m trying to encode this decoded frame with avcodec_encode_audio2 and the codec sets to AV_CODEC_ID_MP3 (I don’t have any codec opening issues) it gives me a segmentation fault (core dumped) whereas everything is allocated... I wonder that perhaps I have too many samples or not enough therefore the encode function is going where nothing is allocated...Probably i have to use some resampling methods but i have no clue.

  Is anyone ever try to encode in mp3 from an input device using the ffmpeg C API and to mux it in a mp3 file or even an avi file ? ( from a microphone)

  The ffmpeg command line works perfectly : ffmpeg -f alsa -i default out.mp3

  Here is my ffmpeg compilation setup with preinstalled stuffs :

  sudo apt-get install libasound2-dev       
  
  sudo apt-get install libmp3lame-dev
  
  
  
  ./configure --disable-static --enable-shared --enable-gpl --enable-libx264 --enable-libv4l2 --enable-gpl --enable-swscale --enable-libmp3lame
  
  
  
  sudo make install
  
  
  
  export LD_LIBRARY_PATH=/usr/local/lib

  Thank you guys !

  Here is the code is used, this is run with pthread after (see main()) :

  #define DEFAULT_AUDIO_INPUT_DRIVER_NAME         "alsa"
  
  #define DEFAULT_AUDIO_INPUT_DEVICE_NAME         "default"
  
  #define DEFAULT_USED_AUDIO_CODEC                AV_CODEC_ID_MP3
  
  #define DEFAULT_OUTPUT_AUDIO_FRAMERATE          44100
  
  #define DEFAULT_AUDIO_OUTPUT_FILE_NAME          "audioTest.mp3"
  
  
  
  
  
  
  
  /* Input and Output audio format.*/
  
  static AVFormatContext *ifmt_ctx = NULL;
  
  static AVFormatContext *ofmt_ctx = NULL; //from video
  
  
  
  /* Codec contexts used to encode input and output. */
  
  static AVCodecContext *dec_ctx = NULL;
  
  static AVCodecContext *enc_ctx = NULL;
  
  
  
  AVPacket audioPacket = { .data = NULL, .size = 0 };
  
  AVPacket audioEncodedPacket = { .data = NULL, .size = 0 };
  
  AVFrame *decodedAudioFrame = NULL;
  
  AVFrame *rescaledAudioFrame = NULL;
  
  AVStream *streamAudio = NULL;
  
  AVCodec *audioEncodeCodec = NULL;
  
  static struct SwrContext *swr_ctx;
  
  
  
  
  
  /* Audio configuration */
  
  char *AUDIO_INPUT_DRIVER_NAME           = {DEFAULT_AUDIO_INPUT_DRIVER_NAME};
  
  char *AUDIO_INPUT_DEVICE_NAME           = {DEFAULT_AUDIO_INPUT_DEVICE_NAME};
  
  enum AVCodecID AUDIO_ENCODED_CODEC_ID   = DEFAULT_USED_AUDIO_CODEC;
  
  int AUDIO_FRAME_RATE                    = DEFAULT_OUTPUT_AUDIO_FRAMERATE;
  
  char* AUDIO_OUTPUT_FILE_NAME            = {DEFAULT_AUDIO_OUTPUT_FILE_NAME};
  
  
  
  static AVFrame *alloc_audio_frame(enum AVSampleFormat sample_fmt,
  
                                    uint64_t channel_layout,
  
                                    int sample_rate, int nb_samples)
  
  {
  
      AVFrame *frame = av_frame_alloc();
  
      int ret;
  
  
  
      if (!frame) {
  
          syslog(LOG_ERR, "Error allocating an audio frame\n");
  
          exit(0);
  
      }
  
  
  
      frame->format = sample_fmt;
  
      frame->channel_layout = channel_layout;
  
      frame->sample_rate = sample_rate;
  
      frame->nb_samples = nb_samples;
  
  
  
      if (nb_samples) {
  
          ret = av_frame_get_buffer(frame, 0);
  
          if (ret < 0) {
  
              syslog(LOG_ERR, "Error allocating an audio buffer\n");
  
              exit(0);
  
          }
  
      }
  
      return frame;
  
  }
  
  
  
  static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt)
  
  {
  
      AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;
  
  
  
     syslog(LOG_INFO, "AUDIO pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
  
             av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),
  
             av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),
  
             av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base), pkt->stream_index);
  
  }
  
  
  
  static int write_frame(AVFormatContext *fmt_ctx, const AVRational *time_base, AVStream *st, AVPacket *pkt)
  
  {
  
      /* rescale output packet timestamp values from codec to stream timebase */
  
      //printf("Write Time Rescale\n");
  
      av_packet_rescale_ts(pkt, *time_base, st->time_base);
  
      pkt->stream_index = st->index;
  
  
  
      /* Write the compressed frame to the media file. */
  
      log_packet(fmt_ctx, pkt);
  
      //printf("Write In File Audio packet size of %d\n", pkt->size);
  
      //return av_interleaved_write_frame(fmt_ctx, pkt);
  
      return av_write_frame(fmt_ctx, pkt);
  
  }
  
  
  
  static void openAudioInput(const char *driverName, const char *deviceName){   
  
      int i; AVInputFormat *file_iformat = NULL;
  
      if((file_iformat = av_find_input_format(driverName)) == NULL){
  
          syslog(LOG_ERR ,"The %s doesn't seem to be registered\n", driverName);
  
          exit(0);
  
      }
  
      /* Open the device, in order to use the audio linux driver. */
  
      if((avformat_open_input(&ifmt_ctx, deviceName, file_iformat, NULL)) < 0){
  
          syslog(LOG_ERR ,"Error while trying to open %s.\n", deviceName);
  
          exit(0);
  
      }
  
      if((avformat_find_stream_info(ifmt_ctx, NULL)) < 0) {
  
          syslog(LOG_ERR, "Cannot find stream information\n");
  
          exit(0);
  
      }
  
      /* Open decoder */
  
      //printf("Number of input stream: %d\n", ifmt_ctx->nb_streams);
  
      /*if(ifmt_ctx->streams[0]->codec->codec_type == AVMEDIA_TYPE_AUDIO)
  
          printf("AUDIO_TYPE\n");*/
  
      for(i = 0; i < ifmt_ctx->nb_streams; i++)
  
          if(ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
  
                  || ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO)
  
              if(avcodec_open2(ifmt_ctx->streams[i]->codec,             
  
              avcodec_find_decoder(ifmt_ctx->streams[i]->codec->codec_id), NULL) < 0){
  
                  syslog(LOG_ERR, "Cannot find stream information\n");
  
                  exit(0);
  
              }
  
      av_dump_format(ifmt_ctx, 1, deviceName, 0);
  
  }
  
  
  
  
  
  static void openAudioOutput(const char *deviceName, const char *fileName, enum AVCodecID encodeCodec){
  
      AVStream *out_stream = NULL, *in_stream = NULL;
  
      AVCodec *encoder;
  
      avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, fileName);
  
      if(!ofmt_ctx){
  
          syslog(LOG_ERR, "Could not create output context\n");
  
          exit(0);
  
      }
  
      out_stream = avformat_new_stream(ofmt_ctx, NULL);
  
      if(!out_stream){
  
          syslog(LOG_ERR, "Failed allocating output stream\n");
  
          exit(0);
  
      }
  
      (ifmt_ctx!=NULL) ? in_stream = ifmt_ctx->streams[0] : exit(0);
  
      dec_ctx = in_stream->codec;
  
      enc_ctx = out_stream->codec;
  
      /* find encoder */
  
      encoder = avcodec_find_encoder(encodeCodec);
  
      enc_ctx->codec = encoder;
  
      /* AUDIO PARAMETERS */
  
      enc_ctx->sample_fmt = encoder->sample_fmts[0];
  
      enc_ctx->bit_rate = 128000; //added
  
  
  
          enc_ctx->sample_rate = dec_ctx->sample_rate;
  
          enc_ctx->channel_layout = AV_CH_LAYOUT_MONO;//dec_ctx->channel_layout;
  
          out_stream->time_base = enc_ctx->time_base = (AVRational){1, enc_ctx->sample_rate};
  
          enc_ctx->channels = av_get_channel_layout_nb_channels(enc_ctx->channel_layout);
  
  
  
      printf("Sample Rate: %d Number Encoded channels: %d\n", dec_ctx->sample_rate, enc_ctx->channels);
  
      /* Open encoder with the found codec */
  
      if(avcodec_open2(enc_ctx, encoder, NULL) < 0) {
  
          syslog(LOG_ERR, "Cannot open audio encoder for stream\n");
  
          exit(0);
  
      }
  
      av_dump_format(ofmt_ctx, 0, fileName, 1);
  
      if (!(ofmt_ctx->oformat->flags & AVFMT_NOFILE))
  
          if(avio_open(&ofmt_ctx->pb, fileName, AVIO_FLAG_WRITE) < 0){
  
              syslog(LOG_ERR, "Could not open output file '%s'", fileName);
  
              exit(0);
  
          }
  
      /* init muxer, write output file header */
  
      if(avformat_write_header(ofmt_ctx, NULL) < 0){
  
          syslog(LOG_ERR, "Error occurred when opening output file\n");
  
          exit(0);
  
      }
  
  
  
  
  
      decodedAudioFrame = av_frame_alloc();
  
      rescaledAudioFrame = av_frame_alloc();
  
  }
  
  
  
  
  
  
  
  void initAudio(void){
  
      openAudioInput(AUDIO_INPUT_DRIVER_NAME, AUDIO_INPUT_DEVICE_NAME);
  
      openAudioOutput(AUDIO_INPUT_DEVICE_NAME, AUDIO_OUTPUT_FILE_NAME, AUDIO_ENCODED_CODEC_ID);
  
  }
  
  
  
  void *audioThread(void){
  
      int16_t *   samples;
  
      int gotDecodedFrame, dst_nb_samples, samples_count=0;
  
      int packetCounter = 0;
  
  
  
      int i = 0, got_packet, got_input, ret;
  
      float sizeOfFile = 0;
  
  
  
      AVPacket packet = { .data = NULL, .size = 0 };
  
  
  
      struct timespec t0, t1;
  
      int flags = fcntl(0, F_GETFL);
  
      flags = fcntl(0, F_SETFL, flags | O_NONBLOCK); //set non-blocking read on stdin
  
      packetCounter = 0;
  
  
  
      do{
  
          clock_gettime(CLOCK_REALTIME, &t0);
  
          if ((av_read_frame(ifmt_ctx, &audioPacket)) < 0){
  
              break;
  
          }
  
          packetCounter++;
  
  
  
          clock_gettime(CLOCK_REALTIME, &t1);
  
          av_init_packet(&audioEncodedPacket);
  
          audioEncodedPacket.data = NULL;
  
          audioEncodedPacket.size = 0;
  
  
  
          if (avcodec_decode_audio4(dec_ctx, decodedAudioFrame, &gotDecodedFrame, &audioPacket) < 0) {
  
              syslog(LOG_ERR ,"Can't Decode the packet received from the camera.\n");
  
              exit(0);
  
          }
  
  
  
          printf("Audio Decoded, Nb Channel %d, Samples per Channel %d, Size %d, PTS %ld\n", 
  
              decodedAudioFrame->channels, 
  
              decodedAudioFrame->nb_samples,
  
              decodedAudioFrame->pkt_size,
  
              decodedAudioFrame->pkt_pts);
  
          /*if((ret = swr_convert(swr_ctx, rescaledAudioFrame->data, rescaledAudioFrame->nb_samples, 
  
          (const uint8_t **)decodedAudioFrame->data, decodedAudioFrame->nb_samples)) < 0){
  
                  syslog(LOG_ERR, "Error while converting\n");
  
                  exit(0);
  
          }*/
  
  
  
          //decodedAudioFrame->pts = audioPacket.pts;//(int64_t)((1.0 / (float)64000) * (float)90 * (float)packetCounter);
  
  
  
          ret = avcodec_encode_audio2(enc_ctx, &audioEncodedPacket, decodedAudioFrame, &got_packet);
  
  
  
  
  
  
  
          printf("Audio encoded packet size = %d, packet nb = %d, sample rate = %d Ret Value = %d\n", audioEncodedPacket.size, packetCounter, enc_ctx->sample_rate, ret);
  
          audioPacket.pts = (int64_t)((1.0 / (float)enc_ctx->sample_rate) * (float)90 * (float)packetCounter);
  
          audioPacket.dts = audioPacket.pts-1;
  
  
  
          ret = write_frame(ofmt_ctx, &enc_ctx->time_base, streamAudio, &audioEncodedPacket);
  
  
  
          av_free_packet(&audioEncodedPacket);
  
  
  
          ssize_t readVal = read(0, &videoAudioThreadExit, 1); // read non-blocking
  
  
  
      }while(videoAudioThreadExit != 'q');
  
  
  
      syslog(LOG_INFO ,"End Audio Thread\n");
  
      return NULL;
  
  }
  
  
  
  
  
  
  
  
  
  
  
  
  
  int main(int argc, char** argv){
  
      int i=0;
  
  
  
      openlog ("TEST", LOG_CONS | LOG_PERROR | LOG_NDELAY, LOG_USER);
  
      syslog (LOG_INFO, "Syslog correctly loaded.\n");
  
      syslog (LOG_INFO, "Program started by user UID %d\n", getuid ());
  
  
  
      av_register_all();
  
      avdevice_register_all();
  
      avcodec_register_all();
  
      avfilter_register_all();
  
  
  
      printf("\n\n\t START GLOBAL INIT\n");
  
      initAudio();
  
  
  
      pthread_create(&t[0], &ctrl[0], (void*)audioThread, NULL);
  
      for(i=0;icode>

• Screen capture with libavcodec/ffmpeg, and write it to mp4 file

  10 février 2015, par Drakkainen

  I’m trying to (programatically) record the screen with DirectShow screen driver. I wrote some quick and (very) dirty code to try to get that to work (http://pastebin.com/ZJuhZRCz) based on ffmpeg examples but I have lots of trouble figuring out what time_base/framerate to use. If i leave the time_base/framerate parts empty I only get a single still frame. If i change them to any values, the video just turns black.

  I’m guessing it has something to do with the output file settings, but I just ran out of ideas on what to try. Any pointers/help would be greatly appreciated.

• FFMPEG with hardware codec support

  28 janvier 2012, par mctma

  I have built a simple media player using ffmpeg on Android 2.2. Hardware is an arm cortex-a8 based 1GHz processor, 512 MB RAM. I am getting low performance, around 15 FPS for 800x600 mp4 video. I have a couple of questions on how I can improve the performance

  • How can I use the hardware codecs available on my target device. How can I configure ffmpeg to use the available hardware decoders ? Does the GPU or graphics driver have to expose some standard API like OpenMax IL in order to this ?

  • What are the options that should be enabled when building ffmpeg so that it can be optimized for my target hardware ? Something like :
    --cpu=cortex=a8 --extra-cflags="-mfpu=neon" ...

  I have already looked around the net but I couldn't find the answers that I am looking for. I hope someone can advice me on this.

  Thanks in advance !