Ignore inactive chains when writing DependencyDescriptor rtp header extension.

To implement rule
"Chains protecting no active decode targets MUST be ignored."
from https://aomediacodec.github.io/av1-rtp-spec/#a44-switching

Bug: webrtc:10342
Change-Id: Ibe5e0b7b6ab8955419d0d9f996c6397f442e1cda
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/177668
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31566}

modules/rtp_rtcp/source/rtp_dependency_descriptor_extension.cc

@@ -10,6 +10,7 @@
 
 #include "modules/rtp_rtcp/source/rtp_dependency_descriptor_extension.h"
 
+#include <bitset>
 #include <cstdint>
 
 #include "api/array_view.h"
@@ -23,6 +24,7 @@ namespace webrtc {
 
 constexpr RTPExtensionType RtpDependencyDescriptorExtension::kId;
 constexpr char RtpDependencyDescriptorExtension::kUri[];
+constexpr std::bitset<32> RtpDependencyDescriptorExtension::kAllChainsAreActive;
 
 bool RtpDependencyDescriptorExtension::Parse(
     rtc::ArrayView<const uint8_t> data,
@@ -34,16 +36,20 @@ bool RtpDependencyDescriptorExtension::Parse(
 
 size_t RtpDependencyDescriptorExtension::ValueSize(
     const FrameDependencyStructure& structure,
+    std::bitset<32> active_chains,
     const DependencyDescriptor& descriptor) {
-  RtpDependencyDescriptorWriter writer(/*data=*/{}, structure, descriptor);
+  RtpDependencyDescriptorWriter writer(/*data=*/{}, structure, active_chains,
+                                       descriptor);
   return DivideRoundUp(writer.ValueSizeBits(), 8);
 }
 
 bool RtpDependencyDescriptorExtension::Write(
     rtc::ArrayView<uint8_t> data,
     const FrameDependencyStructure& structure,
+    std::bitset<32> active_chains,
     const DependencyDescriptor& descriptor) {
-  RtpDependencyDescriptorWriter writer(data, structure, descriptor);
+  RtpDependencyDescriptorWriter writer(data, structure, active_chains,
+                                       descriptor);
   return writer.Write();
 }
 

modules/rtp_rtcp/source/rtp_dependency_descriptor_extension.h

@@ -10,6 +10,7 @@
 #ifndef MODULES_RTP_RTCP_SOURCE_RTP_DEPENDENCY_DESCRIPTOR_EXTENSION_H_
 #define MODULES_RTP_RTCP_SOURCE_RTP_DEPENDENCY_DESCRIPTOR_EXTENSION_H_
 
+#include <bitset>
 #include <cstdint>
 
 #include "api/array_view.h"
@@ -34,10 +35,24 @@ class RtpDependencyDescriptorExtension {
                     DependencyDescriptor* descriptor);
 
   static size_t ValueSize(const FrameDependencyStructure& structure,
+                          const DependencyDescriptor& descriptor) {
+    return ValueSize(structure, kAllChainsAreActive, descriptor);
+  }
+  static size_t ValueSize(const FrameDependencyStructure& structure,
+                          std::bitset<32> active_chains,
                           const DependencyDescriptor& descriptor);
   static bool Write(rtc::ArrayView<uint8_t> data,
                     const FrameDependencyStructure& structure,
+                    const DependencyDescriptor& descriptor) {
+    return Write(data, structure, kAllChainsAreActive, descriptor);
+  }
+  static bool Write(rtc::ArrayView<uint8_t> data,
+                    const FrameDependencyStructure& structure,
+                    std::bitset<32> active_chains,
                     const DependencyDescriptor& descriptor);
+
+ private:
+  static constexpr std::bitset<32> kAllChainsAreActive = ~uint32_t{0};
 };
 
 }  // namespace webrtc

modules/rtp_rtcp/source/rtp_dependency_descriptor_extension_unittest.cc

@@ -63,5 +63,57 @@ TEST(RtpDependencyDescriptorExtensionTest, WriteZeroInUnusedBits) {
   EXPECT_THAT(rtc::MakeArrayView(unused_bytes, num_unused_bytes), Each(0));
 }
 
+// In practice chain diff for inactive chain will grow uboundly because no
+// frames are produced for it, that shouldn't block writing the extension.
+TEST(RtpDependencyDescriptorExtensionTest,
+     TemplateMatchingSkipsInactiveChains) {
+  uint8_t buffer[3];
+  FrameDependencyStructure structure;
+  structure.num_decode_targets = 2;
+  structure.num_chains = 2;
+  structure.templates = {
+      FrameDependencyTemplate().Dtis("SR").ChainDiffs({2, 2})};
+  DependencyDescriptor descriptor;
+  descriptor.frame_dependencies = structure.templates[0];
+
+  // Set only 1st chain as active.
+  std::bitset<32> active_chains = 0b01;
+  descriptor.frame_dependencies.chain_diffs[1] = 1000;
+
+  // Expect perfect template match since the only difference is for an inactive
+  // chain. Pefect template match consumes 3 bytes.
+  EXPECT_EQ(RtpDependencyDescriptorExtension::ValueSize(
+                structure, active_chains, descriptor),
+            3u);
+  EXPECT_TRUE(RtpDependencyDescriptorExtension::Write(
+      buffer, structure, active_chains, descriptor));
+}
+
+TEST(RtpDependencyDescriptorExtensionTest,
+     AcceptsInvalidChainDiffForInactiveChainWhenChainsAreCustom) {
+  uint8_t buffer[256];
+  FrameDependencyStructure structure;
+  structure.num_decode_targets = 2;
+  structure.num_chains = 2;
+  structure.templates = {
+      FrameDependencyTemplate().Dtis("SR").ChainDiffs({2, 2})};
+  DependencyDescriptor descriptor;
+  descriptor.frame_dependencies = structure.templates[0];
+
+  // Set only 1st chain as active.
+  std::bitset<32> active_chains = 0b01;
+  // Set chain_diff different to the template to make it custom.
+  descriptor.frame_dependencies.chain_diffs[0] = 1;
+  // Set chain diff for inactive chain beyound limit of 255 max chain diff.
+  descriptor.frame_dependencies.chain_diffs[1] = 1000;
+
+  // Because chains are custom, should use more than base 3 bytes.
+  EXPECT_GT(RtpDependencyDescriptorExtension::ValueSize(
+                structure, active_chains, descriptor),
+            3u);
+  EXPECT_TRUE(RtpDependencyDescriptorExtension::Write(
+      buffer, structure, active_chains, descriptor));
+}
+
 }  // namespace
 }  // namespace webrtc

modules/rtp_rtcp/source/rtp_dependency_descriptor_writer.cc

@@ -9,6 +9,7 @@
  */
 #include "modules/rtp_rtcp/source/rtp_dependency_descriptor_writer.h"
 
+#include <bitset>
 #include <cstddef>
 #include <cstdint>
 #include <iterator>
@@ -55,9 +56,11 @@ NextLayerIdc GetNextLayerIdc(const FrameDependencyTemplate& previous,
 RtpDependencyDescriptorWriter::RtpDependencyDescriptorWriter(
     rtc::ArrayView<uint8_t> data,
     const FrameDependencyStructure& structure,
+    std::bitset<32> active_chains,
     const DependencyDescriptor& descriptor)
     : descriptor_(descriptor),
       structure_(structure),
+      active_chains_(active_chains),
       bit_writer_(data.data(), data.size()) {
   FindBestTemplate();
 }
@@ -128,8 +131,14 @@ RtpDependencyDescriptorWriter::CalculateMatch(
   result.need_custom_dtis =
       descriptor_.frame_dependencies.decode_target_indications !=
       frame_template->decode_target_indications;
-  result.need_custom_chains =
-      descriptor_.frame_dependencies.chain_diffs != frame_template->chain_diffs;
+  result.need_custom_chains = false;
+  for (int i = 0; i < structure_.num_chains; ++i) {
+    if (active_chains_[i] && descriptor_.frame_dependencies.chain_diffs[i] !=
+                                 frame_template->chain_diffs[i]) {
+      result.need_custom_chains = true;
+      break;
+    }
+  }
 
   result.extra_size_bits = 0;
   if (result.need_custom_fdiffs) {
@@ -366,7 +375,9 @@ void RtpDependencyDescriptorWriter::WriteFrameFdiffs() {
 void RtpDependencyDescriptorWriter::WriteFrameChains() {
   RTC_DCHECK_EQ(descriptor_.frame_dependencies.chain_diffs.size(),
                 structure_.num_chains);
-  for (int chain_diff : descriptor_.frame_dependencies.chain_diffs) {
+  for (int i = 0; i < structure_.num_chains; ++i) {
+    int chain_diff =
+        active_chains_[i] ? descriptor_.frame_dependencies.chain_diffs[i] : 0;
     RTC_DCHECK_GE(chain_diff, 0);
     RTC_DCHECK_LT(chain_diff, 1 << 8);
     WriteBits(chain_diff, 8);

modules/rtp_rtcp/source/rtp_dependency_descriptor_writer.h

@@ -10,6 +10,7 @@
 #ifndef MODULES_RTP_RTCP_SOURCE_RTP_DEPENDENCY_DESCRIPTOR_WRITER_H_
 #define MODULES_RTP_RTCP_SOURCE_RTP_DEPENDENCY_DESCRIPTOR_WRITER_H_
 
+#include <bitset>
 #include <cstddef>
 #include <cstdint>
 #include <vector>
@@ -25,6 +26,7 @@ class RtpDependencyDescriptorWriter {
   // |descriptor| matches the |structure|.
   RtpDependencyDescriptorWriter(rtc::ArrayView<uint8_t> data,
                                 const FrameDependencyStructure& structure,
+                                std::bitset<32> active_chains,
                                 const DependencyDescriptor& descriptor);
 
   // Serializes DependencyDescriptor rtp header extension.
@@ -77,6 +79,7 @@ class RtpDependencyDescriptorWriter {
   bool build_failed_ = false;
   const DependencyDescriptor& descriptor_;
   const FrameDependencyStructure& structure_;
+  std::bitset<32> active_chains_;
   rtc::BitBufferWriter bit_writer_;
   TemplateMatch best_template_;
 };