From 3acaa70965c5570ef1711fee9b3a15eac3e74ffe Mon Sep 17 00:00:00 2001
From: Jean-Marc Valin <jmvalin@amazon.com>
Date: Thu, 30 Jun 2022 20:11:26 -0400
Subject: Adds OPUS_SET_INBAND_FEC(2) option

Unlike OPUS_SET_INBAND_FEC(1), the encoder does not necessarily
switch to SILK if we have music.
---
 include/opus_defines.h |  6 ++++--
 src/opus_encoder.c     | 13 ++++++++-----
 tests/test_opus_api.c  |  2 +-
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/include/opus_defines.h b/include/opus_defines.h
index ceee5b84..94b9e0d9 100644
--- a/include/opus_defines.h
+++ b/include/opus_defines.h
@@ -482,7 +482,8 @@ extern "C" {
   * @param[in] x <tt>opus_int32</tt>: Allowed values:
   * <dl>
   * <dt>0</dt><dd>Disable inband FEC (default).</dd>
-  * <dt>1</dt><dd>Enable inband FEC.</dd>
+  * <dt>1</dt><dd>Inband FEC enabled. If the packet loss rate is sufficiently high, Opus will automatically switch to SILK even at high rates to enable use of that FEC.</dd>
+  * <dt>2</dt><dd>Inband FEC enabled, but does not necessarily switch to SILK if we have music.</dd>
   * </dl>
   * @hideinitializer */
 #define OPUS_SET_INBAND_FEC(x) OPUS_SET_INBAND_FEC_REQUEST, __opus_check_int(x)
@@ -491,7 +492,8 @@ extern "C" {
   * @param[out] x <tt>opus_int32 *</tt>: Returns one of the following values:
   * <dl>
   * <dt>0</dt><dd>Inband FEC disabled (default).</dd>
-  * <dt>1</dt><dd>Inband FEC enabled.</dd>
+  * <dt>1</dt><dd>Inband FEC enabled. If the packet loss rate is sufficiently high, Opus will automatically switch to SILK even at high rates to enable use of that FEC.</dd>
+  * <dt>2</dt><dd>Inband FEC enabled, but does not necessarily switch to SILK if we have music.</dd>
   * </dl>
   * @hideinitializer */
 #define OPUS_GET_INBAND_FEC(x) OPUS_GET_INBAND_FEC_REQUEST, __opus_check_int_ptr(x)
diff --git a/src/opus_encoder.c b/src/opus_encoder.c
index 253fe9e8..64b6726c 100644
--- a/src/opus_encoder.c
+++ b/src/opus_encoder.c
@@ -87,6 +87,7 @@ struct OpusEncoder {
     int          lfe;
     int          arch;
     int          use_dtx;                 /* general DTX for both SILK and CELT */
+    int          fec_config;
 #ifndef DISABLE_FLOAT_API
     TonalityAnalysisState analysis;
 #endif
@@ -1389,8 +1390,9 @@ opus_int32 opus_encode_native(OpusEncoder *st, const opus_val16 *pcm, int frame_
 
        st->mode = (equiv_rate >= threshold) ? MODE_CELT_ONLY: MODE_SILK_ONLY;
 
-       /* When FEC is enabled and there's enough packet loss, use SILK */
-       if (st->silk_mode.useInBandFEC && st->silk_mode.packetLossPercentage > (128-voice_est)>>4)
+       /* When FEC is enabled and there's enough packet loss, use SILK.
+          Unless the FEC is set to 2, in which case we don't switch to SILK if we're confident we have music. */
+       if (st->silk_mode.useInBandFEC && st->silk_mode.packetLossPercentage > (128-voice_est)>>4 && (st->fec_config != 2 || voice_est > 25))
           st->mode = MODE_SILK_ONLY;
        /* When encoding voice and DTX is enabled but the generalized DTX cannot be used,
           use SILK in order to make use of its DTX. */
@@ -2439,11 +2441,12 @@ int opus_encoder_ctl(OpusEncoder *st, int request, ...)
         case OPUS_SET_INBAND_FEC_REQUEST:
         {
             opus_int32 value = va_arg(ap, opus_int32);
-            if(value<0 || value>1)
+            if(value<0 || value>2)
             {
                goto bad_arg;
             }
-            st->silk_mode.useInBandFEC = value;
+            st->fec_config = value;
+            st->silk_mode.useInBandFEC = (value != 0);
         }
         break;
         case OPUS_GET_INBAND_FEC_REQUEST:
@@ -2453,7 +2456,7 @@ int opus_encoder_ctl(OpusEncoder *st, int request, ...)
             {
                goto bad_arg;
             }
-            *value = st->silk_mode.useInBandFEC;
+            *value = st->fec_config;
         }
         break;
         case OPUS_SET_PACKET_LOSS_PERC_REQUEST:
diff --git a/tests/test_opus_api.c b/tests/test_opus_api.c
index fb385c63..0e7ed2cc 100644
--- a/tests/test_opus_api.c
+++ b/tests/test_opus_api.c
@@ -1298,7 +1298,7 @@ opus_int32 test_enc_api(void)
    err=opus_encoder_ctl(enc,OPUS_GET_INBAND_FEC(null_int_ptr));
    if(err!=OPUS_BAD_ARG)test_failed();
    cfgs++;
-   CHECK_SETGET(OPUS_SET_INBAND_FEC(i),OPUS_GET_INBAND_FEC(&i),-1,2,
+   CHECK_SETGET(OPUS_SET_INBAND_FEC(i),OPUS_GET_INBAND_FEC(&i),-1,3,
      1,0,
      "    OPUS_SET_INBAND_FEC .......................... OK.\n",
      "    OPUS_GET_INBAND_FEC .......................... OK.\n")
-- 
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