Currently, we allow webcam/screen capture through MLT's multi consumer so that we can both record and have a preview. However MLT's handling of video4linux devices through FFmpeg is not reliable and causes crashes. So we should try to rewrite audio capture using QtMultimedia.
Audio capture should be easy to implement using the QAudioRecorder class: https://doc.qt.io/qt-5/qaudiorecorder.html
A Vu-Meter should also be quite easy by connecting a QAudioProbe on the QAudioRecorder class. Also, by completely separating the video playback and the audio recording, we might be able to achieve some kind of voiceover feature. Video recording should also be possible in a similar way.
Requirements: Basic C++/Qt knowledge. Does not require knowing too much of Kdenlive's internalls