Merge changes from team/russell/codec_resample

This commit imports libresample for use in Asterisk.  It also adds a new codec
module, codec_resample.  This module uses libresample to re-sample signed linear
audio between 8 kHz and 16 kHz.

It also provides an alternative for converting between 16 kHz G.722 and 8 kHz
signed linear when using G.722, which will likely be useful as some people have
complained about volume issues when the current codec_g722 converts to 8 kHz 
signed linear.  But, to test this, you will have to disable the g722-to-slin and
g722-to-slin16 translators in codec_g722.c.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@95501 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/libresample/README.txt

@@ -0,0 +1,84 @@
+libresample
+
+Real-time library interface by Dominic Mazzoni
+
+Based on resample-1.7:
+  http://www-ccrma.stanford.edu/~jos/resample/
+
+License: LGPL - see the file LICENSE.txt for more information
+
+History:
+
+This library is not the highest-quality resampling library
+available, nor is it the most flexible, nor is it the
+fastest.  But it is pretty good in all of these regards, and
+it is quite portable.  The best resampling library I am aware
+of is libsamplerate by Erik de Castro Lopo.  It's small, fast,
+and very high quality.  However, it uses the GPL for its
+license (with commercial options available) and I needed
+a more free library.  So I wrote this library, using
+the LGPL resample-1.7 library by Julius Smith as a basis.
+
+Resample-1.7 is a fixed-point resampler, and as a result
+has only limited precision.  I rewrote it to use single-precision
+floating-point arithmetic instead and increased the number
+of filter coefficients between time steps significantly.
+On modern processors it can resample in real time even
+with this extra overhead.
+
+Resample-1.7 was designed to read and write from files, so
+I removed all of that code and replaced it with an API that
+lets you pass samples in small chunks.  It should be easy
+to link to resample-1.7 as a library.
+
+Changes in version 0.1.3:
+
+* Fixed two bugs that were causing subtle problems
+  on Intel x86 processors due to differences in roundoff errors.
+
+* Prefixed most function names with lrs and changed header file
+  from resample.h to libresample.h, to avoid namespace
+  collisions with existing programs and libraries.
+
+* Added resample_dup (thanks to Glenn Maynard)
+
+* Argument to resample_get_filter_width takes a const void *
+  (thanks to Glenn Maynard)
+
+* resample-sndfile clips output to -1...1 (thanks to Glenn Maynard)
+
+Usage notes:  
+
+- If the output buffer you pass is too small, resample_process
+  may not use any input samples because its internal output
+  buffer is too full to process any more.  So do not assume
+  that it is an error just because no input samples were
+  consumed.  Just keep passing valid output buffers.
+
+- Given a resampling factor f > 1, and a number of input
+  samples n, the number of output samples should be between
+  floor(n - f) and ceil(n + f).  In other words, if you
+  resample 1000 samples at a factor of 8, the number of
+  output samples might be between 7992 and 8008.  Do not
+  assume that it will be exactly 8000.  If you need exactly
+  8000 outputs, pad the input with extra zeros as necessary.
+
+License and warranty:
+
+All of the files in this package are Copyright 2003 by Dominic
+Mazzoni <dominic@minorninth.com>.  This library was based heavily
+on Resample-1.7, Copyright 1994-2002 by Julius O. Smith III
+<jos@ccrma.stanford.edu>, all rights reserved.
+
+Permission to use and copy is granted subject to the terms of the
+"GNU Lesser General Public License" (LGPL) as published by the
+Free Software Foundation; either version 2.1 of the License,
+or any later version.  In addition, Julius O. Smith III requests
+that a copy of any modified files be sent by email to
+jos@ccrma.stanford.edu so that he may incorporate them into the
+CCRMA version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.