onWarning

Where this source's decoders report a degradation they had to accept and carry on through.

The decoders are the only place that knows, because the knowledge arrives with the frames and not with the container: a stream can start standard dynamic range and change. Colour approximation and a policy-permitted hardware fallback both come out here.

The callback runs on whichever thread called receive, which is the decoder's own thread, so it must be cheap and must not block. Set it before decoding starts. The default discards.

An HLS stream also reports each address it could not read here, those from the open included.