[opus] Impossible two bugs in Opus

[ongaku zettai]

tracked down the spectogram atrefact source; it comes from the resampler.
so it's not really a bug, just a nuisance.
let's hope in the future Opus will be able to save bitrate on simple
audio parts as all other lossy and lossless codecs do.
i think opus decreasing bitrate only when it thinks that audio
is too complex for human to hear difference. that's a bad attitude.