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Merged
lo-simon merged 2 commits into from
Jul 28, 2026
Merged

Support SMPTE 2022-7 temporal redundancy SDP #502

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c56c269
Support SMPTE 2022-7 temporal redundancy SDP
thangldw Jul 14, 2026
87f9ee2
Address temporal redundancy review feedback
thangldw Jul 18, 2026
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1 change: 1 addition & 0 deletions Development/cmake/NmosCppTest.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,7 @@ set(NMOS_CPP_TEST_NMOS_TEST_SOURCES
nmos/test/paging_utils_test.cpp
nmos/test/query_api_test.cpp
nmos/test/sdp_test_utils.cpp
nmos/test/sdp_temporal_redundancy_test.cpp
nmos/test/sdp_utils_test.cpp
nmos/test/settings_test.cpp
nmos/test/slog_test.cpp
Expand Down
154 changes: 144 additions & 10 deletions Development/nmos/sdp_utils.cpp
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
#include "nmos/sdp_utils.h"

#include <limits>
#include <boost/algorithm/string/case_conv.hpp>
#include <boost/asio/ip/address.hpp>
#include <boost/range/adaptor/filtered.hpp>
Expand Down Expand Up @@ -445,6 +446,7 @@ namespace nmos
const auto& destination_ip = nmos::fields::destination_ip(transport_param);
return destination_ip.as_string();
}

}

// Make a json representation of an SDP file, e.g. for sdp::make_session_description, from the specified parameters; explicitly specify whether 'source-filter' attributes are included to override the default behaviour
Expand All @@ -457,8 +459,25 @@ namespace nmos
// and the rtp_enabled status does not affect the leg's media description
// see https://github.com/AMWA-TV/is-05/issues/109#issuecomment-598721418

const bool temporal_redundancy = !sdp_params.temporal_redundancy.synchronization_sources.empty();

if (temporal_redundancy)
{
if (2 != transport_params.size() || 2 != sdp_params.temporal_redundancy.synchronization_sources.size())
{
throw details::sdp_creation_error("SMPTE ST 2022-7 temporal redundancy requires two transport parameter legs and two synchronization sources");
}
if (sdp_params.temporal_redundancy.media_stream_id.empty())
{
throw details::sdp_creation_error("SMPTE ST 2022-7 temporal redundancy requires a media stream id");
}
if (transport_params.at(0) != transport_params.at(1))
{
throw details::sdp_creation_error("SMPTE ST 2022-7 temporal redundancy requires identical transport parameter legs");
}
}
// check to ensure enough media_stream_ids for multi-leg transport_params
if (transport_params.size() > 1 && transport_params.size() > sdp_params.group.media_stream_ids.size())
else if (transport_params.size() > 1 && transport_params.size() > sdp_params.group.media_stream_ids.size())
{
throw details::sdp_creation_error("not enough sdp parameters media stream ids for transport_params");
}
Expand Down Expand Up @@ -684,8 +703,56 @@ namespace nmos
web::json::push_back(media_attributes, fmtp);
}

if (temporal_redundancy)
{
auto synchronization_source_ids = value::array();
for (const auto& synchronization_source : sdp_params.temporal_redundancy.synchronization_sources)
{
web::json::push_back(synchronization_source_ids, value::number(synchronization_source.id));
web::json::push_back(
media_attributes, value_of({
{ sdp::fields::name, sdp::attributes::ssrc },
{ sdp::fields::value, value_of({
{ sdp::fields::ssrc_id, synchronization_source.id },
{ sdp::fields::attribute, value_of({
{ sdp::fields::name, U("cname") },
{ sdp::fields::value, synchronization_source.cname }
}, keep_order) }
}, keep_order) }
}, keep_order)
);
}

web::json::push_back(
media_attributes, value_of({
{ sdp::fields::name, sdp::attributes::ssrc_group },
{ sdp::fields::value, value_of({
{ sdp::fields::semantics, sdp::group_semantics::duplication.name },
{ sdp::fields::ssrc_ids, std::move(synchronization_source_ids) }
}, keep_order) }
}, keep_order)
);

if (sdp_params.temporal_redundancy.duplication_delay)
{
web::json::push_back(
media_attributes, value_of({
{ sdp::fields::name, sdp::attributes::duplication_delay },
{ sdp::fields::value, *sdp_params.temporal_redundancy.duplication_delay }
}, keep_order)
);
}

web::json::push_back(
media_attributes, value_of({
{ sdp::fields::name, sdp::attributes::mid },
{ sdp::fields::value, sdp_params.temporal_redundancy.media_stream_id }
}, keep_order)
);
}

// insert "media stream identification" if there is more than 1 leg
if (transport_params.size() > 1)
if (transport_params.size() > 1 && !temporal_redundancy)
{
// a=mid:<identification-tag>
// See https://tools.ietf.org/html/rfc5888
Expand All @@ -705,6 +772,7 @@ namespace nmos
web::json::push_back(media_descriptions, std::move(media_description));

++leg;
if (temporal_redundancy) break;
}

// add group attribute if there is more than 1 leg
Expand Down Expand Up @@ -954,10 +1022,10 @@ namespace nmos
// * Any Source Multicast
// * Operation with SMPTE 2022-7 - Separate Source Addresses
// * Operation with SMPTE 2022-7 - Separate Destination Addresses
// * Operation with SMPTE 2022-7 - Temporal Redundancy

// The following cases are not yet handled:
// * Operation with SMPTE 2022-5
// * Operation with SMPTE 2022-7 - Temporal Redundancy
// * Operation with RTCP

auto& media_descriptions = sdp::fields::media_descriptions(session_description);
Expand Down Expand Up @@ -1013,10 +1081,21 @@ namespace nmos
// take account of the number of source addresses (cf. Operation with SMPTE 2022-7 - Separate Source Addresses)

auto& media_attributes = sdp::fields::attributes(media_description);
size_t ssrc_duplication_count = 0;
if (!media_attributes.is_null())
{
auto& ma = media_attributes.as_array();

const auto ssrc_group = sdp::find_name(ma, sdp::attributes::ssrc_group);
if (ma.end() != ssrc_group)
{
const auto& value = sdp::fields::value(*ssrc_group);
if (sdp::group_semantics::duplication == sdp::group_semantics_type{ sdp::fields::semantics(value) })
{
ssrc_duplication_count = sdp::fields::ssrc_ids(value).size();
}
}

// hmm, this code assumes that <filter-mode> is 'incl' and ought to check that <nettype>, <address-types> and <dest-address>
// match the connection address, and fall back to any "session-level" source-filter values if they don't match

Expand All @@ -1026,18 +1105,21 @@ namespace nmos
auto& sf = sdp::fields::value(*source_filter);
auto& sa = sdp::fields::source_addresses(sf);

if (sa.size() <= source_address)
if (sa.size() <= source_address && !(1 == sa.size() && source_address < ssrc_duplication_count))
{
source_address -= sa.size();
continue;
}

details::set_multicast_ip_interface_ip(params, sdp::fields::destination_address(sf));
params[nmos::fields::source_ip] = sdp::fields::source_addresses(sf).at(source_address);
params[nmos::fields::source_ip] = sdp::fields::source_addresses(sf).at(1 == sa.size() ? 0 : source_address);
source_address = 0;
}
}

// SSRC-multiplexed temporal redundancy uses one media description for both IS-05 legs.
if (0 != source_address && source_address < ssrc_duplication_count) source_address = 0;

if (0 != source_address)
{
--source_address;
Expand Down Expand Up @@ -1099,11 +1181,9 @@ namespace nmos
}
}

// hmm, this code does not handle Synchronization Source (SSRC) level grouping or attributes
// i.e. the 'ssrc-group' attribute or 'ssrc' used to convey e.g. 'fmtp', 'mediaclk' or 'ts-refclk'
// see https://tools.ietf.org/html/rfc7104#section-3.2
// and https://tools.ietf.org/html/rfc5576
// and https://www.iana.org/assignments/sdp-parameters/sdp-parameters.xhtml#sdp-att-field
// SSRC-level attributes used to convey e.g. 'fmtp', 'mediaclk' or 'ts-refclk' are not handled.
// SSRC-level duplication grouping and cname attributes are handled below.
// See https://www.iana.org/assignments/sdp-parameters/sdp-parameters.xhtml#sdp-att-field

// Group
// a=group:<semantics>[ <identification-tag>]*
Expand All @@ -1125,6 +1205,60 @@ namespace nmos
// See https://tools.ietf.org/html/rfc4566#section-5
const auto& media_descriptions = sdp::fields::media_descriptions(sdp);

// SSRC-level duplication for SMPTE ST 2022-7 temporal redundancy.
// See https://tools.ietf.org/html/rfc5576 and https://tools.ietf.org/html/rfc7104
for (const auto& media_description : media_descriptions.as_array())
{
const auto& media_attributes = sdp::fields::attributes(media_description);
if (media_attributes.is_null()) continue;

const auto& attributes = media_attributes.as_array();
const auto ssrc_group = sdp::find_name(attributes, sdp::attributes::ssrc_group);
if (attributes.end() == ssrc_group) continue;

const auto& ssrc_group_value = sdp::fields::value(*ssrc_group);
if (sdp::group_semantics::duplication != sdp::group_semantics_type{ sdp::fields::semantics(ssrc_group_value) }) continue;
if (2 != sdp::fields::ssrc_ids(ssrc_group_value).size()) continue;
Comment on lines +1219 to +1221

@garethsb garethsb Jul 17, 2026

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This duplicates some of the logic of get_ssrc_duplication_count... but given that function isn't directly usable here, and that means get_ssrc_duplication_count is only used in one place, maybe better to drop that function and inline its code into the single call-site?

@thangldw thangldw Jul 18, 2026 •
edited
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Agreed. Since the helper has a single call site and the temporal-redundancy parser necessarily performs the same group lookup for additional data, keeping the helper does not buy enough reuse. I will remove it and inline the DUP SSRC-group lookup at the transport-parameter call site, while leaving the richer temporal-redundancy parsing logic in its existing layer.


// Separate-source-address redundancy also uses ssrc-group:DUP, but has more than one source address.
const auto source_filter = sdp::find_name(attributes, sdp::attributes::source_filter);
if (attributes.end() != source_filter
&& 1 != sdp::fields::source_addresses(sdp::fields::value(*source_filter)).size()) continue;

for (const auto& id : sdp::fields::ssrc_ids(ssrc_group_value))
{
const auto id_value = id.as_number().to_uint64();
if (id_value > (std::numeric_limits<uint32_t>::max)()) throw std::out_of_range("SSRC id exceeds 32 bits");
utility::string_t cname;
for (const auto& attribute : attributes)
{
if (sdp::attributes::ssrc != sdp::fields::name(attribute)) continue;
const auto& value = sdp::fields::value(attribute);
const auto& source_attribute = sdp::fields::attribute(value);
if (id_value == sdp::fields::ssrc_id(value)
&& U("cname") == sdp::fields::name(source_attribute)
&& !sdp::fields::value(source_attribute).is_null())
{
cname = sdp::fields::value(source_attribute).as_string();
break;
}
}
sdp_params.temporal_redundancy.synchronization_sources.push_back({ static_cast<uint32_t>(id_value), cname });
}

const auto duplication_delay = sdp::find_name(attributes, sdp::attributes::duplication_delay);
if (attributes.end() != duplication_delay)
{
const auto delay = sdp::fields::value(*duplication_delay).as_number().to_uint64();
if (delay > (std::numeric_limits<uint32_t>::max)()) throw std::out_of_range("duplication delay exceeds 32 bits");
sdp_params.temporal_redundancy.duplication_delay = static_cast<uint32_t>(delay);
}

const auto mid = sdp::find_name(attributes, sdp::attributes::mid);
if (attributes.end() != mid) sdp_params.temporal_redundancy.media_stream_id = sdp::fields::value(*mid).as_string();
break;
}

// ts-refclk attributes
// See https://tools.ietf.org/html/rfc7273
sdp_params.ts_refclk = boost::copy_range<std::vector<sdp_parameters::ts_refclk_t>>(media_descriptions.as_array() | boost::adaptors::transformed([&sdp](const value& media_description) -> sdp_parameters::ts_refclk_t
Expand Down
26 changes: 26 additions & 0 deletions Development/nmos/sdp_utils.h
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Expand Up @@ -107,6 +107,7 @@ namespace nmos
// with each RTP sender and receiver.
// When redundancy is being used, the media description and media-level attributes for each stream are assumed
// to be identical except for the values corresponding to the IS-05 transport parameters for each leg.
// SSRC-multiplexed temporal redundancy is represented by one media description and two transport parameter legs.
struct sdp_parameters
{
// Origin ("o=")
Expand Down Expand Up @@ -170,6 +171,31 @@ namespace nmos
group_t(const sdp::group_semantics_type& semantics, const std::vector<utility::string_t>& media_stream_ids) : semantics(semantics), media_stream_ids(media_stream_ids) {}
} group;

// SSRC-level duplication for SMPTE ST 2022-7 temporal redundancy.
// See https://tools.ietf.org/html/rfc5576 and https://tools.ietf.org/html/rfc7104
struct temporal_redundancy_t
{
struct synchronization_source_t
{
uint32_t id;
utility::string_t cname;

synchronization_source_t() : id() {}
synchronization_source_t(uint32_t id, const utility::string_t& cname) : id(id), cname(cname) {}
};

std::vector<synchronization_source_t> synchronization_sources;
bst::optional<uint32_t> duplication_delay;
utility::string_t media_stream_id;

temporal_redundancy_t() {}
temporal_redundancy_t(const std::vector<synchronization_source_t>& synchronization_sources, bst::optional<uint32_t> duplication_delay, const utility::string_t& media_stream_id)
: synchronization_sources(synchronization_sources)
, duplication_delay(duplication_delay)
, media_stream_id(media_stream_id)
{}
} temporal_redundancy;

// Media ("m=")
// See https://tools.ietf.org/html/rfc4566#section-5.14
sdp::media_type media_type;
Expand Down
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