--- res/res_format_attr_celt.c
+++ res/res_format_attr_celt.c
@@ -33,4 +33,10 @@
 
+#include <ctype.h>                      /* for tolower */
+
 #include "asterisk/module.h"
 #include "asterisk/format.h"
+#include "asterisk/astobj2.h"           /* for ao2_ref */
+#include "asterisk/logger.h"            /* for ast_log, LOG_WARNING */
+#include "asterisk/strings.h"           /* for ast_str_append */
+#include "asterisk/utils.h"             /* for MIN */
 
@@ -72,6 +78,7 @@ static int celt_clone(const struct ast_format *src, struct ast_format *dst)
 
 static struct ast_format *celt_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
 {
+	char *attribs = ast_strdupa(attributes), *attrib;
 	struct ast_format *cloned;
 	struct celt_attr *attr;
 	unsigned int val;
@@ -82,7 +89,12 @@ static struct ast_format *celt_parse_sdp_fmtp(const struct ast_format *format, c
 	}
 	attr = ast_format_get_attribute_data(cloned);
 
+	/* lower-case everything, so we are case-insensitive */
+	for (attrib = attribs; *attrib; ++attrib) {
+		*attrib = tolower(*attrib);
+	} /* based on channels/chan_sip.c:process_a_sdp_image() */
+
-	if (sscanf(attributes, "framesize=%30u", &val) == 1) {
+	if (sscanf(attribs, "framesize=%30u", &val) == 1) {
 		attr->framesize = val;
 	}
 
--- res/res_format_attr_h263.c
+++ res/res_format_attr_h263.c
@@ -37,4 +37,8 @@
 
+#include <ctype.h>                      /* for toupper */
+
 #include "asterisk/module.h"
 #include "asterisk/format.h"
+#include "asterisk/strings.h"           /* for ast_str_append */
+#include "asterisk/utils.h"             /* for ast_strip */
 
@@ -156,2 +160,6 @@ static struct ast_format *h263_parse_sdp_fmtp(const struct ast_format *format, c
 	attr = ast_format_get_attribute_data(cloned);
+	/* upper-case everything, so we are case-insensitive */
+	for (attrib = attribs; *attrib; ++attrib) {
+		*attrib = toupper(*attrib);
+	} /* based on channels/chan_sip.c:process_a_sdp_image() */
 
--- res/res_format_attr_opus.c
+++ res/res_format_attr_opus.c
@@ -33,4 +33,7 @@
 
+#include <ctype.h>
+
 #include "asterisk/module.h"
 #include "asterisk/format.h"
+#include "asterisk/astobj2.h"
 #include "asterisk/logger.h"
@@ -136,6 +139,7 @@ static void sdp_fmtp_get(const char *attributes, const char *name, int *attr)
 
 static struct ast_format *opus_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
 {
+	char *attribs = ast_strdupa(attributes), *attrib;
 	struct ast_format *cloned;
 	struct opus_attr *attr;
 
@@ -147,17 +151,22 @@ static struct ast_format *opus_parse_sdp_fmtp(const struct ast_format *format, c
 	attr = ast_format_get_attribute_data(cloned);
 
+	/* lower-case everything, so we are case-insensitive */
+	for (attrib = attribs; *attrib; ++attrib) {
+		*attrib = tolower(*attrib);
+	} /* based on channels/chan_sip.c:process_a_sdp_image() */
+
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_MAX_PLAYBACK_RATE, &attr->maxplayrate);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_MAX_PLAYBACK_RATE, &attr->maxplayrate);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_MAX_CODED_AUDIO_BANDWIDTH,
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_MAX_CODED_AUDIO_BANDWIDTH,
 		&attr->maxplayrate);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_SPROP_MAX_CAPTURE_RATE,
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_SPROP_MAX_CAPTURE_RATE,
 		&attr->spropmaxcapturerate);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_MAX_PTIME, &attr->maxptime);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_MAX_PTIME, &attr->maxptime);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_PTIME, &attr->ptime);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_PTIME, &attr->ptime);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_MAX_AVERAGE_BITRATE, &attr->maxbitrate);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_MAX_AVERAGE_BITRATE, &attr->maxbitrate);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_STEREO, &attr->stereo);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_STEREO, &attr->stereo);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_SPROP_STEREO, &attr->spropstereo);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_SPROP_STEREO, &attr->spropstereo);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_CBR, &attr->cbr);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_CBR, &attr->cbr);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_FEC, &attr->fec);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_FEC, &attr->fec);
-	sdp_fmtp_get(attributes, CODEC_OPUS_ATTR_DTX, &attr->dtx);
+	sdp_fmtp_get(attribs, CODEC_OPUS_ATTR_DTX, &attr->dtx);
 
 	return cloned;
--- res/res_format_attr_silk.c
+++ res/res_format_attr_silk.c
@@ -33,4 +33,9 @@
 
+#include <ctype.h>                      /* for tolower */
+
 #include "asterisk/module.h"
 #include "asterisk/format.h"
+#include "asterisk/logger.h"            /* for ast_log, LOG_WARNING */
+#include "asterisk/strings.h"           /* for ast_str_append */
+#include "asterisk/utils.h"             /* for MAX, MIN */
 
@@ -80,6 +85,7 @@ static int silk_clone(const struct ast_format *src, struct ast_format *dst)
 
 static struct ast_format *silk_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
 {
+	char *attribs = ast_strdupa(attributes), *attrib;
 	struct ast_format *cloned;
 	struct silk_attr *attr;
 	unsigned int val;
@@ -90,13 +96,18 @@ static struct ast_format *silk_parse_sdp_fmtp(const struct ast_format *format, c
 	}
 	attr = ast_format_get_attribute_data(cloned);
 
+	/* lower-case everything, so we are case-insensitive */
+	for (attrib = attribs; *attrib; ++attrib) {
+		*attrib = tolower(*attrib);
+	} /* based on channels/chan_sip.c:process_a_sdp_image() */
+
-	if (sscanf(attributes, "maxaveragebitrate=%30u", &val) == 1) {
+	if (sscanf(attribs, "maxaveragebitrate=%30u", &val) == 1) {
 		attr->maxbitrate = val;
 	}
-	if (sscanf(attributes, "usedtx=%30u", &val) == 1) {
+	if (sscanf(attribs, "usedtx=%30u", &val) == 1) {
 		attr->dtx = val;
 	}
-	if (sscanf(attributes, "useinbandfec=%30u", &val) == 1) {
+	if (sscanf(attribs, "useinbandfec=%30u", &val) == 1) {
 		attr->fec = val;
 	}
 
--- res/res_format_attr_siren14.c
+++ res/res_format_attr_siren14.c
@@ -33,4 +33,9 @@
 
+#include <ctype.h>                      /* for tolower */
+
 #include "asterisk/module.h"
 #include "asterisk/format.h"
+#include "asterisk/astobj2.h"           /* for ao2_bump */
+#include "asterisk/logger.h"            /* for ast_log, LOG_WARNING */
+#include "asterisk/strings.h"           /* for ast_str_append */
 
@@ -47,9 +52,15 @@ static int siren14_clone(const struct ast_format *src, struct ast_format *dst)
 
 static struct ast_format *siren14_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
 {
+	char *attribs = ast_strdupa(attributes), *attrib;
 	unsigned int val;
 
+	/* lower-case everything, so we are case-insensitive */
+	for (attrib = attribs; *attrib; ++attrib) {
+		*attrib = tolower(*attrib);
+	} /* based on channels/chan_sip.c:process_a_sdp_image() */
+
-	if (sscanf(attributes, "bitrate=%30u", &val) == 1) {
+	if (sscanf(attribs, "bitrate=%30u", &val) == 1) {
 		if (val != 48000) {
 			ast_log(LOG_WARNING, "Got siren14 offer at %u bps, but only 48000 bps supported; ignoring.\n", val);
 			return NULL;
--- res/res_format_attr_siren7.c
+++ res/res_format_attr_siren7.c
@@ -33,4 +33,9 @@
 
+#include <ctype.h>                      /* for tolower */
+
 #include "asterisk/module.h"
 #include "asterisk/format.h"
+#include "asterisk/astobj2.h"           /* for ao2_bump */
+#include "asterisk/logger.h"            /* for ast_log, LOG_WARNING */
+#include "asterisk/strings.h"           /* for ast_str_append */
 
@@ -47,9 +52,15 @@ static int siren7_clone(const struct ast_format *src, struct ast_format *dst)
 
 static struct ast_format *siren7_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
 {
+	char *attribs = ast_strdupa(attributes), *attrib;
 	unsigned int val;
 
+	/* lower-case everything, so we are case-insensitive */
+	for (attrib = attribs; *attrib; ++attrib) {
+		*attrib = tolower(*attrib);
+	} /* based on channels/chan_sip.c:process_a_sdp_image() */
+
-	if (sscanf(attributes, "bitrate=%30u", &val) == 1) {
+	if (sscanf(attribs, "bitrate=%30u", &val) == 1) {
 		if (val != 32000) {
 			ast_log(LOG_WARNING, "Got Siren7 offer at %u bps, but only 32000 bps supported; ignoring.\n", val);
 			return NULL;
--- res/res_format_attr_vp8.c
+++ res/res_format_attr_vp8.c
@@ -35,2 +35,4 @@
 
+#include <ctype.h>                      /* for tolower */
+
 #include "asterisk/module.h"
@@ -78,6 +80,7 @@ static int vp8_clone(const struct ast_format *src, struct ast_format *dst)
 
 static struct ast_format *vp8_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
 {
+	char *attribs = ast_strdupa(attributes), *attrib;
 	struct ast_format *cloned;
 	struct vp8_attr *attr;
 	const char *kvp;
@@ -89,13 +92,18 @@ static struct ast_format *vp8_parse_sdp_fmtp(const struct ast_format *format, co
 	}
 	attr = ast_format_get_attribute_data(cloned);
 
+	/* lower-case everything, so we are case-insensitive */
+	for (attrib = attribs; *attrib; ++attrib) {
+		*attrib = tolower(*attrib);
+	} /* based on channels/chan_sip.c:process_a_sdp_image() */
+
-	if ((kvp = strstr(attributes, "max-fr")) && sscanf(kvp, "max-fr=%30u", &val) == 1) {
+	if ((kvp = strstr(attribs, "max-fr")) && sscanf(kvp, "max-fr=%30u", &val) == 1) {
 		attr->maximum_frame_rate = val;
 	} else {
 		attr->maximum_frame_rate = UINT_MAX;
 	}
 
-	if ((kvp = strstr(attributes, "max-fs")) && sscanf(kvp, "max-fs=%30u", &val) == 1) {
+	if ((kvp = strstr(attribs, "max-fs")) && sscanf(kvp, "max-fs=%30u", &val) == 1) {
 		attr->maximum_frame_size = val;
 	} else {
 		attr->maximum_frame_size = UINT_MAX;