This tool shows the capabilities of IPTC's Video Metadata Hub standard. VMHub can be expressed in JSON (as well as other formats). As you enter video metadata into the form, you can see the corresponding VMHub JSON appear.
For more information, see the IPTC Video Metadata Hub pages on iptc.org or the Video Metadata Hub User Guide. Discuss this tool on the public iptc-videometadata email discussion group.