nuxeo-video-viewer plays only audio of video conversion

Steps to reproduce:

1. In a studio project branch, set up XML extension configuring video conversions as found in the attached file conversionConfig.xml
2. In Web UI, create a Video document using the attached file hevc-issue-repro.mp4 using drag-and-drop/Add Properties.
3. If MP4 Orig Optimized was the first conversion to complete, the video element of nuxeo-video-viewer will play only the audio with no visuals.

Note: typically, video elements with a source that has neither audio nor visual playable in the Chrome browser will fall back to the next playable source. However, seeing that Chrome is able to play this conversion's audio, it doesn't fit the "unplayable" criteria and fails to fall back.