Where do you want to add this message? If you want to add it to the video playback screen you really can't, unless you want to make the message part of the video title set by the Title content meta data value:
metaData = {
ContentType: "episode",
Title: "[Video Name] (If this doesn't play...)",
Stream: {
Url: m.appInfo.video_url
},
StreamFormat: m.appInfo.stream_format
}
videoScreen.SetContent( metaData )