In question type essay we can choose the editor type:

When we choose HTML editor with file picker in the response format (essay question settings), with the TinyMCE editor the button audio/video record are not showing in editor:

After debugging I found that in 
tiny_recordrtc/plugininfo::is_enabled we check if return_type exist and not empty in $options
So the problem is that in the renderer of essay question type we are not adding the return type in qtype_essay_format_editorfilepicker_renderer
Here a patch to fix the problem:
 https://github.com/StudiUM/moodle/commit/51aa432caa261fb26705d1289854ec17e9a1abf9