Reland "red: remove special-casing of no-redundancy"

This is a reland of 320c57b7c6bf68d8612a4f135f44b3d29e802113

Original change's description:
> red: remove special-casing of no-redundancy
>
> removes the special-casing of not sending a RED header when there is no redundant payload.
> This avoids switching back and forth between the primary and the red payload format (primarily at the start of the connection).
>
> BUG=webrtc:11640
>
> Change-Id: I8e0044bef1ed7c4168d9527645522392db2ed068
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/220932
> Reviewed-by: Jesus de Vicente Pena <devicentepena@webrtc.org>
> Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
> Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#34703}

Bug: webrtc:11640
Change-Id: I5e5687be575183ee16d74df4a8170e4fedad739f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/228422
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34713}

modules/audio_coding/codecs/red/audio_encoder_copy_red.cc

@@ -122,12 +122,7 @@ AudioEncoder::EncodedInfo AudioEncoderCopyRed::EncodeImpl(
     header_length_bytes += kRedHeaderLength;
   }
 
-  // Allocate room for RFC 2198 header if there is redundant data.
+  // Allocate room for RFC 2198 header.
-  // Otherwise this will send the primary payload type without
-  // wrapping in RED.
-  if (header_length_bytes == kRedLastHeaderLength) {
-    header_length_bytes = 0;
-  }
   encoded->SetSize(header_length_bytes);
 
   // Iterate backwards and append the data.
@@ -148,17 +143,15 @@ AudioEncoder::EncodedInfo AudioEncoderCopyRed::EncodeImpl(
   // `info` will be implicitly cast to an EncodedInfoLeaf struct, effectively
   // discarding the (empty) vector of redundant information. This is
   // intentional.
-  if (header_length_bytes > 0) {
+  if (header_length_bytes > kRedHeaderLength) {
     info.redundant.push_back(info);
     RTC_DCHECK_EQ(info.speech,
                   info.redundant[info.redundant.size() - 1].speech);
   }
 
   encoded->AppendData(primary_encoded_);
-  if (header_length_bytes > 0) {
   RTC_DCHECK_EQ(header_offset, header_length_bytes - 1);
   encoded->data()[header_offset] = info.payload_type;
-  }
 
   // Shift the redundant encodings.
   auto rit = redundant_encodings_.rbegin();
@@ -172,9 +165,7 @@ AudioEncoder::EncodedInfo AudioEncoderCopyRed::EncodeImpl(
   it->second.SetData(primary_encoded_);
 
   // Update main EncodedInfo.
-  if (header_length_bytes > 0) {
   info.payload_type = red_payload_type_;
-  }
   info.encoded_bytes = encoded->size();
   return info;
 }

modules/audio_coding/codecs/red/audio_encoder_copy_red_unittest.cc

@@ -34,6 +34,8 @@ namespace webrtc {
 
 namespace {
 static const size_t kMaxNumSamples = 48 * 10 * 2;  // 10 ms @ 48 kHz stereo.
+static const size_t kRedLastHeaderLength =
+    1;  // 1 byte RED header for the last element.
 }
 
 class AudioEncoderCopyRedTest : public ::testing::Test {
@@ -154,7 +156,7 @@ TEST_F(AudioEncoderCopyRedTest, CheckNoOutput) {
   // First call is a special case, since it does not include a secondary
   // payload.
   EXPECT_EQ(0u, encoded_info_.redundant.size());
-  EXPECT_EQ(kEncodedSize, encoded_info_.encoded_bytes);
+  EXPECT_EQ(kEncodedSize + kRedLastHeaderLength, encoded_info_.encoded_bytes);
 
   // Next call to the speech encoder will not produce any output.
   Encode();
@@ -190,7 +192,7 @@ TEST_F(AudioEncoderCopyRedTest, CheckPayloadSizesSingle) {
   // payload.
   Encode();
   EXPECT_EQ(0u, encoded_info_.redundant.size());
-  EXPECT_EQ(1u, encoded_info_.encoded_bytes);
+  EXPECT_EQ(kRedLastHeaderLength + 1u, encoded_info_.encoded_bytes);
 
   for (size_t i = 2; i <= kNumPackets; ++i) {
     Encode();
@@ -217,7 +219,7 @@ TEST_F(AudioEncoderCopyRedTest, CheckPayloadSizes) {
   // payload.
   Encode();
   EXPECT_EQ(0u, encoded_info_.redundant.size());
-  EXPECT_EQ(1u, encoded_info_.encoded_bytes);
+  EXPECT_EQ(kRedLastHeaderLength + 1u, encoded_info_.encoded_bytes);
 
   // Second call is also special since it does not include a tertiary
   // payload.
@@ -259,7 +261,7 @@ TEST_F(AudioEncoderCopyRedTest, CheckPayloadSizesTriple) {
   // payload.
   Encode();
   EXPECT_EQ(0u, encoded_info_.redundant.size());
-  EXPECT_EQ(1u, encoded_info_.encoded_bytes);
+  EXPECT_EQ(kRedLastHeaderLength + 1u, encoded_info_.encoded_bytes);
 
   // Second call is also special since it does not include a tertiary
   // payload.
@@ -329,9 +331,10 @@ TEST_F(AudioEncoderCopyRedTest, CheckPayloads) {
   // First call is a special case, since it does not include a secondary
   // payload.
   Encode();
-  EXPECT_EQ(kPayloadLenBytes, encoded_info_.encoded_bytes);
+  EXPECT_EQ(kRedLastHeaderLength + kPayloadLenBytes,
+            encoded_info_.encoded_bytes);
   for (size_t i = 0; i < kPayloadLenBytes; ++i) {
-    EXPECT_EQ(i, encoded_.data()[i]);
+    EXPECT_EQ(i, encoded_.data()[kRedLastHeaderLength + i]);
   }
 
   for (int j = 0; j < 1; ++j) {