channel.c: Allow generic plc then channel formats are equal

If the two formats on a channel are equal, we don't transcode and since
the generic plc needs slin to work, it doesn't get invoked.

* A new configuration option "genericplc_on_equal_codecs" was added
  to the "plc" section of codecs.conf to allow generic packet loss
  concealment even if no transcoding was originally needed.
  Transcoding via SLIN is forced in this case.

ASTERISK-27743

Change-Id: I0577026a179dea34232e63123254b4e0508378f4

6 files changed, 35 insertions, 4 deletions

diff --git a/CHANGES b/CHANGES
index 0f4ced2af..09a7659d4 100644
--- a/CHANGES
+++ b/CHANGES
@@ -101,6 +101,13 @@ Core:
 --- Functionality changes from Asterisk 15.3.0 to Asterisk 15.4.0 ------------
 ------------------------------------------------------------------------------
 
+Core
+------------------
+ * A new configuration option "genericplc_on_equal_codecs" was added to the
+   "plc" section of codecs.conf to allow generic packet loss concealment even
+   if no transcoding was originally needed.  Transcoding via SLIN is forced
+   in this case.
+
 res_pjproject
 ------------------
  * Added the "cache_pools" option to pjproject.conf.  Disabling the option
diff --git a/configs/samples/codecs.conf.sample b/configs/samples/codecs.conf.sample
index 8457fb5ac..8c9ce6631 100644
--- a/configs/samples/codecs.conf.sample
+++ b/configs/samples/codecs.conf.sample
@@ -64,8 +64,15 @@ experimental_rtcp_feedback => false
 [plc]
 ; for all codecs which do not support native PLC
 ; this determines whether to perform generic PLC
-; there is a minor performance penalty for this
+; there is a minor performance penalty for this.
+; By default plc is applied only when the 2 codecs
+; in a channel are different.
 genericplc => true
+; Apply generic plc to channels even if the 2 codecs
+; are the same.  This forces transcoding via slin so
+; the performance impact should be considered.
+; Ignored if genericplc is not also enabled.
+genericplc_on_equal_codecs => false
 
 ; Generate custom formats for formats requiring attributes.
 ; After defining the custom format, the name used in defining
diff --git a/include/asterisk/options.h b/include/asterisk/options.h
index 78f596a88..fc366caa5 100644
--- a/include/asterisk/options.h
+++ b/include/asterisk/options.h
@@ -98,6 +98,8 @@ enum ast_option_flags {
 	AST_OPT_FLAG_LOCK_CONFIG_DIR = (1 << 29),
 	/*! Generic PLC */
 	AST_OPT_FLAG_GENERIC_PLC = (1 << 30),
+	/*! Generic PLC onm equal codecs */
+	AST_OPT_FLAG_GENERIC_PLC_ON_EQUAL_CODECS = (1 << 31),
 };
 
 /*! These are the options that set by default when Asterisk starts */
@@ -134,6 +136,7 @@ enum ast_option_flags {
 #define ast_opt_lock_confdir		ast_test_flag(&ast_options, AST_OPT_FLAG_LOCK_CONFIG_DIR)
 #define ast_opt_generic_plc         ast_test_flag(&ast_options, AST_OPT_FLAG_GENERIC_PLC)
 #define ast_opt_ref_debug           ast_test_flag(&ast_options, AST_OPT_FLAG_REF_DEBUG)
+#define ast_opt_generic_plc_on_equal_codecs  ast_test_flag(&ast_options, AST_OPT_FLAG_GENERIC_PLC_ON_EQUAL_CODECS)
 
 /*! Maximum log level defined by PJPROJECT. */
 #define MAX_PJ_LOG_MAX_LEVEL		6
diff --git a/main/asterisk.c b/main/asterisk.c
index 2a7e30166..89fc441cb 100644
--- a/main/asterisk.c
+++ b/main/asterisk.c
@@ -599,6 +599,7 @@ static char *handle_show_settings(struct ast_cli_entry *e, int cmd, struct ast_c
 	ast_cli(a->fd, "  Transcode via SLIN:          %s\n", ast_test_flag(&ast_options, AST_OPT_FLAG_TRANSCODE_VIA_SLIN) ? "Enabled" : "Disabled");
 	ast_cli(a->fd, "  Transmit silence during rec: %s\n", ast_test_flag(&ast_options, AST_OPT_FLAG_TRANSMIT_SILENCE) ? "Enabled" : "Disabled");
 	ast_cli(a->fd, "  Generic PLC:                 %s\n", ast_test_flag(&ast_options, AST_OPT_FLAG_GENERIC_PLC) ? "Enabled" : "Disabled");
+	ast_cli(a->fd, "  Generic PLC on equal codecs: %s\n", ast_test_flag(&ast_options, AST_OPT_FLAG_GENERIC_PLC_ON_EQUAL_CODECS) ? "Enabled" : "Disabled");
 	ast_cli(a->fd, "  Min DTMF duration::          %u\n", option_dtmfminduration);
 #if !defined(LOW_MEMORY)
 	ast_cli(a->fd, "  Cache media frames:          %s\n", ast_opt_cache_media_frames ? "Enabled" : "Disabled");
diff --git a/main/channel.c b/main/channel.c
index c7847cbd4..8325f19c3 100644
--- a/main/channel.c
+++ b/main/channel.c
@@ -6485,11 +6485,15 @@ static int ast_channel_make_compatible_helper(struct ast_channel *from, struct a
 	 * to use SLINEAR between channels, but only if there is
 	 * no direct conversion available. If generic PLC is
 	 * desired, then transcoding via SLINEAR is a requirement
+	 * even if the formats are the same.
 	 */
-	if (ast_format_cmp(best_dst_fmt, best_src_fmt) == AST_FORMAT_CMP_NOT_EQUAL
-		&& (ast_opt_generic_plc || ast_opt_transcode_via_slin)) {
+	if (ast_opt_generic_plc_on_equal_codecs
+		|| (ast_format_cmp(best_dst_fmt, best_src_fmt) == AST_FORMAT_CMP_NOT_EQUAL
+			&& (ast_opt_generic_plc || ast_opt_transcode_via_slin))) {
+
 		int use_slin = (ast_format_cache_is_slinear(best_src_fmt)
-			|| ast_format_cache_is_slinear(best_dst_fmt)) ? 1 : 0;
+			|| ast_format_cache_is_slinear(best_dst_fmt))
+			? 1 : ast_opt_generic_plc_on_equal_codecs;
 
 		if (use_slin || ast_translate_path_steps(best_dst_fmt, best_src_fmt) != 1) {
 			int best_sample_rate = (ast_format_get_sample_rate(best_src_fmt) > ast_format_get_sample_rate(best_dst_fmt)) ?
diff --git a/main/plc.c b/main/plc.c
index 847ce65b0..369d285a5 100644
--- a/main/plc.c
+++ b/main/plc.c
@@ -262,10 +262,19 @@ static int reload_module(void)
 	for (var = ast_variable_browse(cfg, "plc"); var; var = var->next) {
 		if (!strcasecmp(var->name, "genericplc")) {
 			ast_set2_flag(&ast_options, ast_true(var->value), AST_OPT_FLAG_GENERIC_PLC);
+		} else if (!strcasecmp(var->name, "genericplc_on_equal_codecs")) {
+			ast_set2_flag(&ast_options, ast_true(var->value), AST_OPT_FLAG_GENERIC_PLC_ON_EQUAL_CODECS);
 		}
 	}
 	ast_config_destroy(cfg);
 
+	/*
+	 * Force on_equal_codecs to false if generic_plc is false.
+	 */
+	if (!ast_opt_generic_plc) {
+		ast_set2_flag(&ast_options, 0, AST_OPT_FLAG_GENERIC_PLC_ON_EQUAL_CODECS);
+	}
+
 	return 0;
 }