This treats mono as planar internally within libavresample rather
than changing the sample format.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

This allows reordering, duplication, and silencing of input channels.

This is more consistent with what the rest of Libav does.

This breaks API.

Signed-off-by: Martin Storsjö <martin@martin.st>

This is a new library for audio sample format, channel layout, and sample rate
conversion.