Command line audio recorder and player using ffmpeg API / C++

Software requirements:
A command line C++ application that let user choose an audio input device, an audio output device and then record 5 seconds of audio from the selected input device.
The recording should be kept in memory, encoded using the opus encoder.
Then the user can choose to playback the recording from memory to the selected audio output device.
Audio input/output selection and recording/playback should be implemented using the ffmpeg library.
I have already implemented the menu logic.
Download the Qt C++ project from this link: https://www.sendspace.com/file/p4t56x

These four functions should be implemented:
1.
void MainMenu::list_audio_input_devices()
{
//list all audio input devices [1...n] (mic, line-in etc)
std::cout << "List of all audio input devices" << std::endl;
}

2.
void MainMenu::list_audio_output_devices()
{
//list all audio output devices [1...n] (speaker, ext out etc)
std::cout << "List of all audio output devices" << std::endl;
}

3.
void MainMenu::record_audio_5secs()
{
//Record audio for 5 seconds, from the selected selectedAudioInputDevice.
//Encode audio using the opus encoder and keep it in memory
std::cout << "Begin recording audio for 5 seconds" << std::endl;
std::cout << "Encode audio in memory using the opus encoder" << std::endl;
std::cout << "Recording complete!" << std::endl;
}

4.
void MainMenu::playback_audio_from_memory()
{
//Playback audio from memory to the selected selectedAudioOutputDevice.
std::cout << "Playing audio..." << std::endl;
std::cout << "Done!" << std::endl;
}