There is a known problem with TechSmith Relay 4.0.0 or earlier that causes Speech to Text to fail. If the source presentation from the Recorder does not contain audio, the Speech to Text engine will be unable to transcribe the audio. This will result in a failed job within Presentation > Job Status. Deleting this transcription job on Camtasia Relay will not remove the video, but will simply remove the transcription attempted by the service. Camtasia Relay will then move onto encoding and publishing the content based on your profile settings.
The behavior when source presentation is audioless has been updated in version 4.2.0. Now, if the source video does not contain audio, the transcription attempt will be skipped.