DRM key sessions

When the player encounters a piece of encrypted content for which it does not have a key, it requires a licence containing the required key from SSP using an authorisation token. Some pieces of content require multiple keys, for example:

• A different key may be required for the content at different times (key rotation).

• Different parts of the content may require different keys (video and audio, or alternative video tracks for different angles or resolutions).

Making multiple licence requests can be problematic. In many configurations, the authorisation token may only be used once; subsequent licence requests using the same token will fail, causing playback to fail.

To overcome this issue, where content needs a different key for different tracks, the licence returned by SSP will contain the required keys for all tracks. To play the content, with multiSession configuration set to false (default), the player makes a single licence request and creates a single key session containing all the keys.

This approach is not suitable for key rotation, so the player must be configured for multiple key sessions and makes a licence request every time a new key is required, with multiSession configuration is set to true. 

let playerInstance = otvplayer("videoPlayer",
    // options
    {
        plugins: {
            otvtoolkit: {
                drm:  {
                    config: {
                        ...
                        multiSession: true
                    }
                }
            }
        }
    },
    // loaded callback
    function loadedCallback() {
    ...
    }
);