[Libav-user] FFPEG: Errors opening audio input stream on MacOs

[Xavier Valls Pla]

I am encountering the following warning (from [Audio Toolbox][1]?) very often when opening an external microphone audio stream with libavformat on macOS (M2, Sonoma 14.5):

`CMIO_Unit_Converter_Audio.cpp:590:RebuildAudioConverter AudioConverterSetProperty(dbca) failed (1886547824)`

This warning results on the codec id of the stream not being properly detected and it defaulting to the dummy AV_CODEC_ID_FIRST_AUDIO, which defaults to AV_CODEC_ID_PCM_S16LE, and results on distorted audio decoding the packet when this is not the correct codec.

You can observe the error with the following code (change the value of inputDevice to your device of choice), where I open and close and input audio stream 10 times in a row. Except for the internal macbook microphone, all the other ones I tried error more times than succeed, some only succeeding on the first call. From what I can tell, all these microphones correct detected codec with this code is AV_CODEC_ID_PCM_F32LE.

=================
#include "libavdevice/avdevice.h"
#include "libavformat/avformat.h"
#include <stdio.h>

const char inputDevice[] = ":0";

int main(int argc, char *argv[]) {
  const AVInputFormat *inputFormat;
  AVStream *inputStream = NULL;
  AVFormatContext *inputFormatContext = NULL;
  int ret;
  int i, j;

  // Initialize the input
  avdevice_register_all();

  inputFormat = av_find_input_format("avfoundation");

  for (i = 0; i < 10; i++) {
    ret = avformat_open_input(&inputFormatContext, inputDevice, inputFormat,
                              NULL);
    if (ret != 0) {
      fprintf(stderr, "Couldn't open input audio device");
      break;
    }

    ret = avformat_find_stream_info(inputFormatContext, NULL);
    if (ret < 0) {
      fprintf(stderr, "Couldn't find stream information.");
      break;
    }

    for (j = 0; j < inputFormatContext->nb_streams; j++) {
      if (inputFormatContext->streams[j]->codecpar->codec_type ==
          AVMEDIA_TYPE_AUDIO) {
        inputStream = inputFormatContext->streams[j];
        break;
      }
    }
    if (!inputStream) {
      fprintf(stderr, "Couldn't find a audio stream.");
      break;
    }
    printf("codecID: %s\n",
           inputStream->codecpar->codec_id == AV_CODEC_ID_FIRST_AUDIO
               ? "Incorrect"
               : "Correct");
    avformat_close_input(&inputFormatContext);
  }
  return 0;
}
=================

Example output:

codecID: Correct
codecID: Incorrect
codecID: Incorrect
codecID: Incorrect
codecID: Incorrect
codecID: Correct
codecID: Incorrect
codecID: Incorrect
codecID: Incorrect
codecID: Correct


How can avoid the warning? What am I doing wrong?


  [1]: https://developer.apple.com/documentation/audiotoolbox/audio_converter_services?language=objc
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