The QuickDraw vout is gone since  a long time so this remnant is a NO-OP

We need to know it before MediaCodec is started.

Try a delayed opening only if csd changed.

Allocating and reading 100 MiB at once for a remote file was a bit
excessive IMHO.

If there is a parent input, it cannot go away. There was no point in
reference counting.

This is arguably the only case where the callback made sense.

(The read callback is as suspicious and retained.)