RTP: Enable AMR codec.

Change-Id: I49e6bdc1b67306b44173f2f346f8372a50264870

2 files changed, 173 insertions, 0 deletions

diff --git a/voip/jni/rtp/AmrCodec.cpp b/voip/jni/rtp/AmrCodec.cpp
index 9a2227d..f3ecac2 100644
--- a/voip/jni/rtp/AmrCodec.cpp
+++ b/voip/jni/rtp/AmrCodec.cpp
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include <string.h>
+
 #include "AudioCodec.h"
 
 #include "gsmamr_dec.h"
@@ -21,6 +23,170 @@
 
 namespace {
 
+const int gFrameBits[8] = {95, 103, 118, 134, 148, 159, 204, 244};
+
+//------------------------------------------------------------------------------
+
+// See RFC 4867 for the encoding details.
+
+class AmrCodec : public AudioCodec
+{
+public:
+    AmrCodec() {
+        if (AMREncodeInit(&mEncoder, &mSidSync, false)) {
+            mEncoder = NULL;
+        }
+        if (GSMInitDecode(&mDecoder, (Word8 *)"RTP")) {
+            mDecoder = NULL;
+        }
+    }
+
+    ~AmrCodec() {
+        if (mEncoder) {
+            AMREncodeExit(&mEncoder, &mSidSync);
+        }
+        if (mDecoder) {
+            GSMDecodeFrameExit(&mDecoder);
+        }
+    }
+
+    int set(int sampleRate, const char *fmtp);
+    int encode(void *payload, int16_t *samples);
+    int decode(int16_t *samples, void *payload, int length);
+
+private:
+    void *mEncoder;
+    void *mSidSync;
+    void *mDecoder;
+
+    int mMode;
+    int mModeSet;
+    bool mOctetAligned;
+};
+
+int AmrCodec::set(int sampleRate, const char *fmtp)
+{
+    // These parameters are not supported.
+    if (strcasestr(fmtp, "crc=1") || strcasestr(fmtp, "robust-sorting=1") ||
+        strcasestr(fmtp, "interleaving=")) {
+        return -1;
+    }
+
+    // Handle mode-set and octet-align.
+    char *modes = strcasestr(fmtp, "mode-set=");
+    if (modes) {
+        mMode = 0;
+        mModeSet = 0;
+        for (char c = *modes; c && c != ' '; c = *++modes) {
+            if (c >= '0' && c <= '7') {
+                int mode = c - '0';
+                if (mode > mMode) {
+                    mMode = mode;
+                }
+                mModeSet |= 1 << mode;
+            }
+        }
+    } else {
+        mMode = 7;
+        mModeSet = 0xFF;
+    }
+    mOctetAligned = (strcasestr(fmtp, "octet-align=1") != NULL);
+
+    // TODO: handle mode-change-*.
+
+    return (sampleRate == 8000 && mEncoder && mDecoder) ? 160 : -1;
+}
+
+int AmrCodec::encode(void *payload, int16_t *samples)
+{
+    unsigned char *bytes = (unsigned char *)payload;
+    Frame_Type_3GPP type;
+
+    int length = AMREncode(mEncoder, mSidSync, (Mode)mMode,
+        samples, bytes + 1, &type, AMR_TX_WMF);
+
+    if (type != mMode || length != (8 + gFrameBits[mMode] + 7) >> 3) {
+        return -1;
+    }
+
+    if (mOctetAligned) {
+        bytes[0] = 0xF0;
+        bytes[1] = (mMode << 3) | 0x04;
+        ++length;
+    } else {
+        // CMR = 15 (4-bit), F = 0 (1-bit), FT = mMode (4-bit), Q = 1 (1-bit).
+        bytes[0] = 0xFF;
+        bytes[1] = 0xC0 | (mMode << 1) | 1;
+
+        // Shift left 6 bits and update the length.
+        bytes[length + 1] = 0;
+        for (int i = 0; i <= length; ++i) {
+            bytes[i] = (bytes[i] << 6) | (bytes[i + 1] >> 2);
+        }
+        length = (10 + gFrameBits[mMode] + 7) >> 3;
+    }
+    return length;
+}
+
+int AmrCodec::decode(int16_t *samples, void *payload, int length)
+{
+    unsigned char *bytes = (unsigned char *)payload;
+    Frame_Type_3GPP type;
+    if (length < 2) {
+        return -1;
+    }
+    int request = bytes[0] >> 4;
+
+    if (mOctetAligned) {
+        if ((bytes[1] & 0xC4) != 0x04) {
+            return -1;
+        }
+        type = (Frame_Type_3GPP)(bytes[1] >> 3);
+        if (length != (16 + gFrameBits[type] + 7) >> 3) {
+            return -1;
+        }
+        length -= 2;
+        bytes += 2;
+    } else {
+        if ((bytes[0] & 0x0C) || !(bytes[1] & 0x40)) {
+            return -1;
+        }
+        type = (Frame_Type_3GPP)((bytes[0] << 1 | bytes[1] >> 7) & 0x07);
+        if (length != (10 + gFrameBits[type] + 7) >> 3) {
+            return -1;
+        }
+
+        // Shift left 2 bits and update the length.
+        --length;
+        for (int i = 1; i < length; ++i) {
+            bytes[i] = (bytes[i] << 2) | (bytes[i + 1] >> 6);
+        }
+        bytes[length] <<= 2;
+        length = (gFrameBits[type] + 7) >> 3;
+        ++bytes;
+    }
+
+    if (AMRDecode(mDecoder, type, bytes, samples, MIME_IETF) != length) {
+        return -1;
+    }
+
+    // Handle CMR
+    if (request < 8 && request != mMode) {
+        for (int i = request; i >= 0; --i) {
+            if (mModeSet & (1 << i)) {
+                mMode = request;
+                break;
+            }
+        }
+    }
+
+    return 160;
+}
+
+//------------------------------------------------------------------------------
+
+// See RFC 3551 for the encoding details.
+
 class GsmEfrCodec : public AudioCodec
 {
 public:
@@ -91,6 +257,11 @@ int GsmEfrCodec::decode(int16_t *samples, void *payload, int length)
 
 } // namespace
 
+AudioCodec *newAmrCodec()
+{
+    return new AmrCodec;
+}
+
 AudioCodec *newGsmEfrCodec()
 {
     return new GsmEfrCodec;
diff --git a/voip/jni/rtp/AudioCodec.cpp b/voip/jni/rtp/AudioCodec.cpp
index afc193c..2267ea0 100644
--- a/voip/jni/rtp/AudioCodec.cpp
+++ b/voip/jni/rtp/AudioCodec.cpp
@@ -21,6 +21,7 @@
 extern AudioCodec *newAlawCodec();
 extern AudioCodec *newUlawCodec();
 extern AudioCodec *newGsmCodec();
+extern AudioCodec *newAmrCodec();
 extern AudioCodec *newGsmEfrCodec();
 
 struct AudioCodecType {
@@ -30,6 +31,7 @@ struct AudioCodecType {
     {"PCMA", newAlawCodec},
     {"PCMU", newUlawCodec},
     {"GSM", newGsmCodec},
+    {"AMR", newAmrCodec},
     {"GSM-EFR", newGsmEfrCodec},
     {NULL, NULL},
 };