The one for which invalid was returned was only 60k. I was hoping for an official response from someone at Roku. I really don't feel like experimenting and no matter how you look at it GetMetaData is just plain flawed.
sound = CreateObject("roAudioResource", "pkg:/assets/audio/cartoon002.wav")
print "Sound is "+type(sound)
"Sound is Invalid"
BrightScript Debugger> res=createobject("roAudioResource","pkg:/images/cartoon002.wav")
BrightScript Debugger> ?type(res)
BrightScript Debugger> res.trigger(100)
BrightScript Debugger> print listdir("pkg:/assets/audio/")
OK, so my BrightScript project didn't automatically include the additional directories!
Strangely, I am able to put the audio file into /images/ and it loads fine as roAudioResource.
If I use /assets/audio/ then it still remains Invalid - even if I make sure to include that path in the build (export).