lavfi/showspectrum: set default height to 512

Only power-of-two FFTs are supported; so to get a full spectrum
(that is, one up to Nyquist), the height must be a power of two.

Therefore, change the default height from 480 to 512.

Signed-off-by: Rudolf Polzer <divverent@xonotic.org>
qdm2: Fix data type used in multiplication.

Avoid unintended truncation.
Fixes CID700555

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
qdm2: disable superblocktype_2_3==0 code

The code is untested and contained bugs, we need a sample if any files
use this branch.

Suggested-by: Roberto Togni
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>