mgcp: Add RTP audio transcoding
This patch implements audio transcoding between the formats GSM,
PCMA, L16, and optionally G.729.
The feature needs to be enabled by using the autoconf option
'--enable-mgcp-transcoding'. In this case mgcp_transcode.c will
be compiled and linked to osmo-bsc_mgcp, and the transcoding
functions provided will be registered as processing callbacks.
If G.729 support is required, libcg729 needs to be installed and
'--with-g729' must be passed to ./configure.
Ticket: OW#1111
Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/osmo-bsc_mgcp/g711common.h b/openbsc/src/osmo-bsc_mgcp/g711common.h
new file mode 100644
index 0000000..cb35fc6
--- /dev/null
+++ b/openbsc/src/osmo-bsc_mgcp/g711common.h
@@ -0,0 +1,187 @@
+/*
+ * PCM - A-Law conversion
+ * Copyright (c) 2000 by Abramo Bagnara <abramo@alsa-project.org>
+ *
+ * Wrapper for linphone Codec class by Simon Morlat <simon.morlat@linphone.org>
+ *
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+static inline int val_seg(int val)
+{
+ int r = 0;
+ val >>= 7; /*7 = 4 + 3*/
+ if (val & 0xf0) {
+ val >>= 4;
+ r += 4;
+ }
+ if (val & 0x0c) {
+ val >>= 2;
+ r += 2;
+ }
+ if (val & 0x02)
+ r += 1;
+ return r;
+}
+
+/*
+ * s16_to_alaw() - Convert a 16-bit linear PCM value to 8-bit A-law
+ *
+ * s16_to_alaw() accepts an 16-bit integer and encodes it as A-law data.
+ *
+ * Linear Input Code Compressed Code
+ * ------------------------ ---------------
+ * 0000000wxyza 000wxyz
+ * 0000001wxyza 001wxyz
+ * 000001wxyzab 010wxyz
+ * 00001wxyzabc 011wxyz
+ * 0001wxyzabcd 100wxyz
+ * 001wxyzabcde 101wxyz
+ * 01wxyzabcdef 110wxyz
+ * 1wxyzabcdefg 111wxyz
+ *
+ * For further information see John C. Bellamy's Digital Telephony, 1982,
+ * John Wiley & Sons, pps 98-111 and 472-476.
+ * G711 is designed for 13 bits input signal, this function add extra shifting to take this into account.
+ */
+
+static inline unsigned char s16_to_alaw(int pcm_val)
+{
+ int mask;
+ int seg;
+ unsigned char aval;
+
+ if (pcm_val >= 0) {
+ mask = 0xD5;
+ } else {
+ mask = 0x55;
+ pcm_val = -pcm_val;
+ if (pcm_val > 0x7fff)
+ pcm_val = 0x7fff;
+ }
+
+ if (pcm_val < 256) /*256 = 32 << 3*/
+ aval = pcm_val >> 4; /*4 = 1 + 3*/
+ else {
+ /* Convert the scaled magnitude to segment number. */
+ seg = val_seg(pcm_val);
+ aval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f);
+ }
+ return aval ^ mask;
+}
+
+/*
+ * alaw_to_s16() - Convert an A-law value to 16-bit linear PCM
+ *
+ */
+static inline int alaw_to_s16(unsigned char a_val)
+{
+ int t;
+ int seg;
+
+ a_val ^= 0x55;
+ t = a_val & 0x7f;
+ if (t < 16)
+ t = (t << 4) + 8;
+ else {
+ seg = (t >> 4) & 0x07;
+ t = ((t & 0x0f) << 4) + 0x108;
+ t <<= seg -1;
+ }
+ return ((a_val & 0x80) ? t : -t);
+}
+/*
+ * s16_to_ulaw() - Convert a linear PCM value to u-law
+ *
+ * In order to simplify the encoding process, the original linear magnitude
+ * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
+ * (33 - 8191). The result can be seen in the following encoding table:
+ *
+ * Biased Linear Input Code Compressed Code
+ * ------------------------ ---------------
+ * 00000001wxyza 000wxyz
+ * 0000001wxyzab 001wxyz
+ * 000001wxyzabc 010wxyz
+ * 00001wxyzabcd 011wxyz
+ * 0001wxyzabcde 100wxyz
+ * 001wxyzabcdef 101wxyz
+ * 01wxyzabcdefg 110wxyz
+ * 1wxyzabcdefgh 111wxyz
+ *
+ * Each biased linear code has a leading 1 which identifies the segment
+ * number. The value of the segment number is equal to 7 minus the number
+ * of leading 0's. The quantization interval is directly available as the
+ * four bits wxyz. * The trailing bits (a - h) are ignored.
+ *
+ * Ordinarily the complement of the resulting code word is used for
+ * transmission, and so the code word is complemented before it is returned.
+ *
+ * For further information see John C. Bellamy's Digital Telephony, 1982,
+ * John Wiley & Sons, pps 98-111 and 472-476.
+ */
+
+static inline unsigned char s16_to_ulaw(int pcm_val) /* 2's complement (16-bit range) */
+{
+ int mask;
+ int seg;
+ unsigned char uval;
+
+ if (pcm_val < 0) {
+ pcm_val = 0x84 - pcm_val;
+ mask = 0x7f;
+ } else {
+ pcm_val += 0x84;
+ mask = 0xff;
+ }
+ if (pcm_val > 0x7fff)
+ pcm_val = 0x7fff;
+
+ /* Convert the scaled magnitude to segment number. */
+ seg = val_seg(pcm_val);
+
+ /*
+ * Combine the sign, segment, quantization bits;
+ * and complement the code word.
+ */
+ uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0x0f);
+ return uval ^ mask;
+}
+
+/*
+ * ulaw_to_s16() - Convert a u-law value to 16-bit linear PCM
+ *
+ * First, a biased linear code is derived from the code word. An unbiased
+ * output can then be obtained by subtracting 33 from the biased code.
+ *
+ * Note that this function expects to be passed the complement of the
+ * original code word. This is in keeping with ISDN conventions.
+ */
+static inline int ulaw_to_s16(unsigned char u_val)
+{
+ int t;
+
+ /* Complement to obtain normal u-law value. */
+ u_val = ~u_val;
+
+ /*
+ * Extract and bias the quantization bits. Then
+ * shift up by the segment number and subtract out the bias.
+ */
+ t = ((u_val & 0x0f) << 3) + 0x84;
+ t <<= (u_val & 0x70) >> 4;
+
+ return ((u_val & 0x80) ? (0x84 - t) : (t - 0x84));
+}