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• How do I convert ADPCM to PCM using FFmpeg ?

  26 janvier 2013, par mystafer

  I have a video feed that sends me audio using the ADPCM codec. However, android only supports PCM format. How can I convert the ADPCM audio feed into a PCM audio feed ?

  The answer to this may be similar to the answer to this question.

  I have successfully decoded the frame with this code :

  int len = avcodec_decode_audio4(pAudioCodecCtx, pAudioFrame, &frameFinished, &packet);

  Is the secret here to use a reverse encode function ?

  Here is what I have so far in my audio decode function :

  if(packet_queue_get(env, javaThread, pAudioPacketQueue, &packet, 1) < 0) {
  
      LOGE("audio - after get packet failed");
  
      return;
  
  }
  
  LOGD("Dequeued audio packet");
  
  
  
  // calculate frame size
  
  int frameSize;
  
  if (pPcmAudioCodecCtx->frame_size) {
  
      frameSize = pPcmAudioCodecCtx->frame_size;
  
  } else {
  
      /* if frame_size is not set, the number of samples must be
  
       * calculated from the buffer size */
  
      int64_t nb_samples = (int64_t)AUDIO_PCM_OUTBUFF_SIZE * 8 /
  
              (av_get_bits_per_sample(pPcmAudioCodecCtx->codec_id) *
  
                      pPcmAudioCodecCtx->channels);
  
      frameSize = nb_samples;
  
  }
  
  
  
  int pcmBytesPerSample = av_get_bytes_per_sample(pPcmAudioCodecCtx->sample_fmt);
  
  int pcmFrameBytes = frameSize * pcmBytesPerSample * pPcmAudioCodecCtx->channels;
  
  
  
  uint8_t *pDataStart = packet.data;
  
  while(packet.size > 0) {
  
      int len = avcodec_decode_audio4(pAudioCodecCtx, pAudioFrame, &frameFinished, &packet);
  
      LOGD("Decoded ADPCM frame");
  
  
  
      if (len < 0) {
  
          LOGE("Error while decoding audio");
  
          return;
  
      }
  
  
  
      if (frameFinished) {
  
          // store frame data in FIFO buffer
  
          uint8_t *inputBuffer = pAudioFrame->data[0];
  
          int inputBufferSize = pAudioFrame->linesize[0];
  
          av_fifo_generic_write(fifoBuffer, inputBuffer, inputBufferSize, NULL);
  
          LOGD("Added ADPCM frame to FIFO buffer");
  
  
  
          // check if fifo buffer has enough data for a PCM frame
  
          while (av_fifo_size(fifoBuffer) >= pcmFrameBytes) {
  
              LOGI("PCM frame data in FIFO buffer");
  
  
  
              // read frame's worth of data from FIFO buffer
  
              av_fifo_generic_read(fifoBuffer, pAudioPcmOutBuffer, pcmFrameBytes, NULL);
  
              LOGD("Read data from FIFO buffer into pcm frame");
  
  
  
  
  
              avcodec_get_frame_defaults(pPcmAudioFrame);
  
              LOGD("Got frame defaults");
  
  
  
              pPcmAudioFrame->nb_samples = pcmFrameBytes / (pPcmAudioCodecCtx->channels *
  
                      pcmBytesPerSample);
  
  
  
              avcodec_fill_audio_frame(pPcmAudioFrame, pPcmAudioCodecCtx->channels,
  
                      pPcmAudioCodecCtx->sample_fmt,
  
                      pAudioPcmOutBuffer, pcmFrameBytes, 1);
  
              LOGD("Filled frame audio with data");
  
  
  
              // fill audio play buffer
  
              int dataSize = pPcmAudioFrame->linesize[0];
  
              LOGD("Data to output: %d", dataSize);
  
              jbyteArray audioPlayBuffer = (jbyteArray) env->GetObjectField(ffmpegCtx, env->GetFieldID(cls, "audioPlayBuffer", "[B"));
  
              jbyte *bytes = env->GetByteArrayElements(audioPlayBuffer, NULL);
  
              memcpy(bytes, pPcmAudioFrame->data[0], dataSize);
  
              env->ReleaseByteArrayElements(audioPlayBuffer, bytes, 0);
  
              LOGD("Copied data into Java array");
  
  
  
              env->CallVoidMethod(player, env->GetMethodID(playerCls, "updateAudio", "(I)V"), dataSize);
  
          }

• Decoding video frames and sending them to RabbitMQ using FFmpeg

  28 janvier 2023, par viator

  I've built ffmpeg with AMQP support and tried ffmpeg -i /videos/episode.mp4 -f mpegts amqp://localhost which apparently works. But AFAIK mpegts has some muxing overhead, so I don't really know how it splits stream into messages.

  


  Is it possible to decode all the frames from a video and send them one-by-one in some format (say, JPEG or PNG) to RabbitMQ ?

  


• Making Sure The PNG Gets There

  14 juin 2013, par Multimedia Mike — General

  Rewind to 1999. I was developing an HTTP-based remote management interface for an embedded device. The device sat on an ethernet LAN and you could point a web browser at it. The pitch was to transmit an image of the device’s touch screen and the user could click on the picture to interact with the device. So we needed an image format. If you were computing at the time, you know that the web was insufferably limited back then. Our choice basically came down to GIF and JPEG. Being the office’s annoying free software zealot, I was championing a little known up and coming format named PNG.

  So the challenge was to create our own PNG encoder (incorporating a library like libpng wasn’t an option for this platform). I seem to remember being annoyed at having to implement an integrity check (CRC) for the PNG encoder. It’s part of the PNG spec, after all. It just seemed so redundant. At the time, I reasoned that there were 5 layers of integrity validation in play.

  I don’t know why, but I was reflecting on this episode recently and decided to revisit it. Here are all the encapsulation layers of a PNG file when flung over an ethernet network :

  
  
  

  So there are up to 5 encapsulations for the data in this situation. At the innermost level is the image data which is compressed with the zlib DEFLATE method. At first, I thought that this also had a CRC or checksum. However, in researching this post, I couldn’t find any evidence of such an integrity check. Further, I don’t think we bothered to compress the PNG data in this project long ago. It was a small image, monochrome, and transferring via LAN, so the encoder could get away with signaling uncompressed data.

  The graphical data gets wrapped up in a PNG chunk and all PNG chunks have a CRC. To transmit via the network, it goes into a TCP frame, which also has a checksum. That goes into an IP packet. I previously believed that this represented another integrity check. While an IP frame does have a checksum, the checksum only covers the IP header and not the payload. So that doesn’t really count towards this goal.

  Finally, the data gets encapsulated into an ethernet frame which has — you guessed it — a CRC.

  I see that other link layer protocols like PPP and wireless ethernet (802.11) also feature frame CRCs. So I guess what I’m saying is that, if you transfer a PNG file over the network, you can be confident that the data will be free of any errors.