如何在Linux上使用带有ffmpeg的C ++从USB音频设备录制音频？

Question

How can I record an audio from USB audio device using C++ with ffmpeg on Linux? I have the following code. But I have no idea how to set the parameter of 'url' in the function of avformat_open_input. Could assistance be provided by anybody? Much appreciated.

   27     av_register_all();
   28     avdevice_register_all();
   29
   30     //pAudioInputFmt =av_find_input_format("dshow");
   31     pAudioInputFmt =av_find_input_format("alsa");
   32     //assert(pAudioInputFmt != NULL);
   33     if (!(pAudioInputFmt != NULL))
   34     {
   35         printf("Error %s %d\n", __FILE__, __LINE__);
   36         char ch = cin.get();
   37         cout << "ch = "<< ch << endl;
   38         return (-1);
   39     }
   40
   41     // I have no idear how to set the second parameter on Linux.
   42     if (!(avformat_open_input(&pFmtCtx, "=Device)", pAudioInputFmt,NULL) == 0))
   43     {
   44         printf("Error %s %d\n", __FILE__, __LINE__);
   45         system("pause");
   46         return (-1);
   47     }

Answer 1

Have you read this example of demuxing and decoding audio and video? By using only the audio part and filtering out what you don't need, you should be able to record audio.

Also, what do you get when executing

arecord -l

in the terminal? Given that you get something like

card x: USB audio

try to give "hw:x" as the input, where x is the number of the card given by the arecord -l command. In my case the USB microphone is card 1, so I give "hw:1" as the input to FFmpeg.