Transcription text for a marked audio can be generated by invoking transcription service.
To transcribe an audio block, first select a non-transcribed block by double clicking on it which will mark (select) the audio piece and then click "Create text for marker audio" option in top menu edit drop down. This will open a dialog box.
In the opened dialog, select a service provider and language of the audio input from the drop down lists. Providing speaker name is optional.
Click "Transcribe" to start the process.