RecordRTC v5.3.0

Relevant commit: 3a2276e

Now MRecordRTC can NOT only pass mimeType but also StereoAudioRecorder/MediaStreamRecorder.

recorder.mediaType = {
   audio: StereoAudioRecorder,
   video: MediaStreamRecorder
};

// mimeType is optional and should be set only in advance cases.
recorder.mimeType = {
    audio: 'audio/wav',
    video: 'video/webm',
    gif:   'image/gif'
};