Thumbnails
When you upload media to your project, thumbnails for each media file are created after the file is uploaded. Thumbnails are stored in the cloud, never locally.
It may take between a few seconds and a couple minutes for your thumbnail to appear, depending on system load.
Uploading Your Own Thumbnails
If you are an app developer see how to upload a thumbnail in the Flow Production Tracking API and a technical overview of Flow Production Tracking Events to work with thumbnails.
In order for thumbnail media to be visible in the Flow Production Tracking interface, they must be uploaded. Images can be saved to local filesystems as an attachment, but they must be stored in the cloud and processed by the transcoder to have any thumbnails and viewable/playable media in the Flow Production Tracking interface.