in RtpPacketizer add support for first packet reduction length

Bug: webrtc:9680
Change-Id: I68580a8a44cbbf932ed0b2448b31169b26df5044
Reviewed-on: https://webrtc-review.googlesource.com/98005
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24584}

modules/rtp_rtcp/source/rtp_format.cc

@@ -65,11 +65,15 @@ std::unique_ptr<RtpPacketizer> RtpPacketizer::Create(
 std::vector<size_t> RtpPacketizer::SplitAboutEqually(
     size_t payload_len,
     const PayloadSizeLimits& limits) {
+  RTC_CHECK_GT(limits.max_payload_len, limits.first_packet_reduction_len);
   RTC_CHECK_GT(limits.max_payload_len, limits.last_packet_reduction_len);
 
-  // Last packet can be smaller. Pretend that it's the same size, but we must
-  // write more payload to it.
-  size_t total_bytes = payload_len + limits.last_packet_reduction_len;
+  // First and last packet of the frame can be smaller. Pretend that it's
+  // the same size, but we must write more payload to it.
+  // Assume frame fits in single packet if packet has extra space for sum
+  // of first and last packets reductions.
+  size_t total_bytes = payload_len + limits.first_packet_reduction_len +
+                       limits.last_packet_reduction_len;
   // Integer divisions with rounding up.
   size_t num_packets_left =
       (total_bytes + limits.max_payload_len - 1) / limits.max_payload_len;
@@ -79,12 +83,19 @@ std::vector<size_t> RtpPacketizer::SplitAboutEqually(
 
   std::vector<size_t> result;
   result.reserve(num_packets_left);
+  bool first_packet = true;
   while (remaining_data > 0) {
     // Last num_larger_packets are 1 byte wider than the rest. Increase
     // per-packet payload size when needed.
     if (num_packets_left == num_larger_packets)
       ++bytes_per_packet;
     size_t current_packet_bytes = bytes_per_packet;
+    if (first_packet) {
+      if (current_packet_bytes > limits.first_packet_reduction_len + 1)
+        current_packet_bytes -= limits.first_packet_reduction_len;
+      else
+        current_packet_bytes = 1;
+    }
     if (current_packet_bytes > remaining_data) {
       current_packet_bytes = remaining_data;
     }
@@ -93,11 +104,11 @@ std::vector<size_t> RtpPacketizer::SplitAboutEqually(
     if (num_packets_left == 2 && current_packet_bytes == remaining_data) {
       --current_packet_bytes;
     }
-
     result.push_back(current_packet_bytes);
 
     remaining_data -= current_packet_bytes;
     --num_packets_left;
+    first_packet = false;
   }
 
   return result;

modules/rtp_rtcp/source/rtp_format.h

@@ -28,6 +28,7 @@ class RtpPacketizer {
  public:
   struct PayloadSizeLimits {
     size_t max_payload_len = 1200;
+    size_t first_packet_reduction_len = 0;
     size_t last_packet_reduction_len = 0;
   };
   static std::unique_ptr<RtpPacketizer> Create(

modules/rtp_rtcp/source/rtp_format_unittest.cc

@@ -21,6 +21,7 @@ namespace {
 
 using ::testing::ElementsAre;
 using ::testing::Le;
+using ::testing::Gt;
 using ::testing::Each;
 using ::testing::IsEmpty;
 using ::testing::Not;
@@ -66,6 +67,20 @@ TEST(RtpPacketizerSplitAboutEqually, AllPacketsAreEqualRespectsMaxPayloadSize) {
   EXPECT_THAT(payload_sizes, Each(Le(limits.max_payload_len)));
 }
 
+TEST(RtpPacketizerSplitAboutEqually,
+     AllPacketsAreEqualRespectsFirstPacketReduction) {
+  RtpPacketizer::PayloadSizeLimits limits;
+  limits.max_payload_len = 5;
+  limits.first_packet_reduction_len = 2;
+
+  std::vector<size_t> payload_sizes =
+      RtpPacketizer::SplitAboutEqually(13, limits);
+
+  ASSERT_THAT(payload_sizes, Not(IsEmpty()));
+  EXPECT_EQ(payload_sizes.front() + limits.first_packet_reduction_len,
+            limits.max_payload_len);
+}
+
 TEST(RtpPacketizerSplitAboutEqually,
      AllPacketsAreEqualRespectsLastPacketReductionLength) {
   RtpPacketizer::PayloadSizeLimits limits;
@@ -115,7 +130,8 @@ TEST(RtpPacketizerSplitAboutEqually, SomePacketsAreSmallerSumToPayloadLen) {
   EXPECT_THAT(Sum(payload_sizes), 28);
 }
 
-TEST(RtpPacketizerVideoGeneric, SomePacketsAreSmallerRespectsMaxPayloadSize) {
+TEST(RtpPacketizerSplitAboutEqually,
+     SomePacketsAreSmallerRespectsMaxPayloadSize) {
   RtpPacketizer::PayloadSizeLimits limits;
   limits.max_payload_len = 7;
   limits.last_packet_reduction_len = 5;
@@ -126,7 +142,20 @@ TEST(RtpPacketizerVideoGeneric, SomePacketsAreSmallerRespectsMaxPayloadSize) {
   EXPECT_THAT(payload_sizes, Each(Le(limits.max_payload_len)));
 }
 
-TEST(RtpPacketizerVideoGeneric,
+TEST(RtpPacketizerSplitAboutEqually,
+     SomePacketsAreSmallerRespectsFirstPacketReduction) {
+  RtpPacketizer::PayloadSizeLimits limits;
+  limits.max_payload_len = 7;
+  limits.first_packet_reduction_len = 5;
+
+  std::vector<size_t> payload_sizes =
+      RtpPacketizer::SplitAboutEqually(28, limits);
+
+  EXPECT_LE(payload_sizes.front() + limits.first_packet_reduction_len,
+            limits.max_payload_len);
+}
+
+TEST(RtpPacketizerSplitAboutEqually,
      SomePacketsAreSmallerRespectsLastPacketReductionLength) {
   RtpPacketizer::PayloadSizeLimits limits;
   limits.max_payload_len = 7;
@@ -139,7 +168,8 @@ TEST(RtpPacketizerVideoGeneric,
             limits.max_payload_len - limits.last_packet_reduction_len);
 }
 
-TEST(RtpPacketizerVideoGeneric, SomePacketsAreSmallerPacketsAlmostEqualInSize) {
+TEST(RtpPacketizerSplitAboutEqually,
+     SomePacketsAreSmallerPacketsAlmostEqualInSize) {
   RtpPacketizer::PayloadSizeLimits limits;
   limits.max_payload_len = 7;
   limits.last_packet_reduction_len = 5;
@@ -150,7 +180,7 @@ TEST(RtpPacketizerVideoGeneric, SomePacketsAreSmallerPacketsAlmostEqualInSize) {
   EXPECT_LE(EffectivePacketsSizeDifference(payload_sizes, limits), 1);
 }
 
-TEST(RtpPacketizerVideoGeneric,
+TEST(RtpPacketizerSplitAboutEqually,
      SomePacketsAreSmallerGeneratesMinimumNumberOfPackets) {
   RtpPacketizer::PayloadSizeLimits limits;
   limits.max_payload_len = 7;
@@ -164,5 +194,43 @@ TEST(RtpPacketizerVideoGeneric,
   EXPECT_THAT(payload_sizes, SizeIs(5));
 }
 
+TEST(RtpPacketizerSplitAboutEqually, GivesNonZeroPayloadLengthEachPacket) {
+  RtpPacketizer::PayloadSizeLimits limits;
+  limits.max_payload_len = 600;
+  limits.first_packet_reduction_len = 500;
+  limits.last_packet_reduction_len = 550;
+
+  // Naive implementation would split 1450 payload + 1050 reduction bytes into 5
+  // packets 500 bytes each, thus leaving first packet zero bytes and even less
+  // to last packet.
+  std::vector<size_t> payload_sizes =
+      RtpPacketizer::SplitAboutEqually(1450, limits);
+
+  EXPECT_EQ(Sum(payload_sizes), 1450u);
+  EXPECT_THAT(payload_sizes, Each(Gt(0u)));
+}
+
+TEST(RtpPacketizerSplitAboutEqually,
+     OnePacketWhenExtraSpaceIsEnoughForSumOfFirstAndLastPacketReductions) {
+  RtpPacketizer::PayloadSizeLimits limits;
+  limits.max_payload_len = 30;
+  limits.first_packet_reduction_len = 6;
+  limits.last_packet_reduction_len = 4;
+
+  EXPECT_THAT(RtpPacketizer::SplitAboutEqually(20, limits), ElementsAre(20));
+}
+
+TEST(RtpPacketizerSplitAboutEqually,
+     TwoPacketsWhenExtraSpaceIsTooSmallForSumOfFirstAndLastPacketReductions) {
+  RtpPacketizer::PayloadSizeLimits limits;
+  limits.max_payload_len = 29;
+  limits.first_packet_reduction_len = 6;
+  limits.last_packet_reduction_len = 4;
+
+  // First packet needs two more extra bytes compared to last one,
+  // so should have two less payload bytes.
+  EXPECT_THAT(RtpPacketizer::SplitAboutEqually(20, limits), ElementsAre(9, 11));
+}
+
 }  // namespace
 }  // namespace webrtc