If the matrix results in an output channel not getting a contribution
from any input channel and the corresponding input channel does not
contribute to any outputs, we can skip the channel during mixing and
silence it after mixing.

If the matrix results in an input channel not contributing to any output
channels and it is not in the output mix, or if the input channel only
contributes fully to the same output channel, we can skip the channel
during mixing.

If the matrix results in an output channel only getting full
contribution from the corresponding input channel and that input channel
does not contribute to any other output channels, we can skip the
channel during mixing.

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

Simplifies header dependencies by not including all other internal headers
in internal.h.

If a bug exists on the tracker, its ID should always be included
in fix messages.

Also, any relevant bug fixes should be CC'd to libav-stable, so
we can actually track what needs to be backported, instead of
just randomly combing the git history and old CVEs.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

It's obviously undesireable to blindly allocate memory based on
a damaged 'size' value, for example.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

It's pretty much the best tool for the job, and it's what we
all use now anyway.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

We obviously prefer git-send-email(1), and the disjointed nature
of the two statements was misleading.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

Signed-off-by: Diego Biurrun <diego@biurrun.de>

Plug an annoying memory leak on broken files.

Snow is a toy codec with no real-world use and horrible code.

255 to 174 cycles on Arrandale / Win64. Unrolling yields no gain.
Signed-off-by: Diego Biurrun <diego@biurrun.de>

698 to 174 cycles on Arrandale. Unrolling is a 6 cycles gain.
Signed-off-by: Diego Biurrun <diego@biurrun.de>