When you upload a video to TrainTool, it gets encoded to the right format for playback to participants. This encoding process takes a while, so after uploading, you won't see the video directly. When you save the page and come back after a while, you will see a thumbnail of your video. This period increases as the file size increases.
If your video doesn't show up at all, please check the file name: don't use punctuation marks or brackets in the file name, as this may break the encoding process. Safe to use: letters, numbers. dashes (-) and underscores (_).