By default, the DRACO decoder will be loaded from a Google CDN on-demand. The decoder is open source and distributed for free under the Apache License 2.0.
It is possible to customize where the decoder is loaded from by defining a global configuration option like so:
When customizing the decoder location, you must make sure that the configuration is set before the first <model-viewer> element is created on the page. <model-viewer> will attempt to load the decoder as soon as it loads a glTF that uses the DRACO extension, so be careful to set the configuration early!
Another way to set the decoder location is to look up the constructor for <model-viewer> and configure it directly:
Note that the direct configuration approach will only work after <model-viewer> is defined in the browser (in typical cases, after model-viewer.js has been loaded).
Keep in mind that the DRACO decoder is pretty large (more than 100KB), so it is best only to use DRACO compressed models when the file size savings are larger than the size of the decoder.