Chromium Code Reviews
chromiumcodereview-hr@appspot.gserviceaccount.com (chromiumcodereview-hr) | Please choose your nickname with Settings | Help | Chromium Project | Gerrit Changes | Sign out
(30)

Unified Diff: webrtc/modules/rtp_rtcp/source/ulpfec_header_reader_writer.cc

Issue 2260803002: Generalize FEC header formatting. (pt. 4) (Closed) Base URL: https://chromium.googlesource.com/external/webrtc.git@master
Patch Set: Lint fix. Created 4 years, 3 months ago
Use n/p to move between diff chunks; N/P to move between comments. Draft comments are only viewable by you.
Jump to:
View side-by-side diff with in-line comments
Download patch
Index: webrtc/modules/rtp_rtcp/source/ulpfec_header_reader_writer.cc
diff --git a/webrtc/modules/rtp_rtcp/source/ulpfec_header_reader_writer.cc b/webrtc/modules/rtp_rtcp/source/ulpfec_header_reader_writer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..2913482554c4b58c095de97129d1a57d9cc06e2e
--- /dev/null
+++ b/webrtc/modules/rtp_rtcp/source/ulpfec_header_reader_writer.cc
@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/rtp_rtcp/source/ulpfec_header_reader_writer.h"
+
+#include <utility>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/modules/rtp_rtcp/source/byte_io.h"
+#include "webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h"
+
+namespace webrtc {
+
+namespace {
+
+// Maximum number of media packets that can be protected in one batch.
+constexpr size_t kMaxMediaPackets = 48;
+
+// Maximum number of FEC packets stored inside ForwardErrorCorrection.
+constexpr size_t kMaxFecPackets = kMaxMediaPackets;
+
+// FEC Level 0 header size in bytes.
+constexpr size_t kFecLevel0HeaderSize = 10;
+
+// FEC Level 1 (ULP) header size in bytes (L bit is set).
+constexpr size_t kFecLevel1HeaderSizeLBitSet = 2 + kUlpfecPacketMaskSizeLBitSet;
+
+// FEC Level 1 (ULP) header size in bytes (L bit is cleared).
+constexpr size_t kFecLevel1HeaderSizeLBitClear =
+ 2 + kUlpfecPacketMaskSizeLBitClear;
+
+constexpr size_t kPacketMaskOffset = kFecLevel0HeaderSize + 2;
+
+size_t UlpfecHeaderSize(size_t packet_mask_size) {
+ RTC_DCHECK_LE(packet_mask_size, kUlpfecPacketMaskSizeLBitSet);
+ if (packet_mask_size <= kUlpfecPacketMaskSizeLBitClear) {
+ return kFecLevel0HeaderSize + kFecLevel1HeaderSizeLBitClear;
+ } else {
+ return kFecLevel0HeaderSize + kFecLevel1HeaderSizeLBitSet;
+ }
+}
+
+} // namespace
+
+UlpfecHeaderReader::UlpfecHeaderReader()
+ : FecHeaderReader(kMaxMediaPackets, kMaxFecPackets) {}
+
+UlpfecHeaderReader::~UlpfecHeaderReader() = default;
+
+bool UlpfecHeaderReader::ReadFecHeader(
+ ForwardErrorCorrection::ReceivedFecPacket* fec_packet) const {
+ bool l_bit = (fec_packet->pkt->data[0] & 0x40) != 0u;
+ size_t packet_mask_size =
+ l_bit ? kUlpfecPacketMaskSizeLBitSet : kUlpfecPacketMaskSizeLBitClear;
+ fec_packet->fec_header_size = UlpfecHeaderSize(packet_mask_size);
+ uint16_t seq_num_base =
+ ByteReader<uint16_t>::ReadBigEndian(&fec_packet->pkt->data[2]);
+ fec_packet->protected_ssrc = fec_packet->ssrc; // Due to RED.
+ fec_packet->seq_num_base = seq_num_base;
+ fec_packet->packet_mask_offset = kPacketMaskOffset;
+ fec_packet->packet_mask_size = packet_mask_size;
+ fec_packet->protection_length =
+ ByteReader<uint16_t>::ReadBigEndian(&fec_packet->pkt->data[10]);
+
+ // Store length recovery field in temporary location in header.
+ // This makes the header "compatible" with the corresponding
+ // FlexFEC location of the length recovery field, thus simplifying
+ // the XORing operations.
+ memcpy(&fec_packet->pkt->data[2], &fec_packet->pkt->data[8], 2);
+
+ return true;
+}
+
+UlpfecHeaderWriter::UlpfecHeaderWriter()
+ : FecHeaderWriter(kMaxMediaPackets,
+ kMaxFecPackets,
+ kFecLevel0HeaderSize + kFecLevel1HeaderSizeLBitSet) {}
+
+UlpfecHeaderWriter::~UlpfecHeaderWriter() = default;
+
+// TODO(brandtr): Consider updating this implementation (which actually
+// returns a bound on the sequence number spread), if logic is added to
+// UlpfecHeaderWriter::FinalizeFecHeader to truncate packet masks which end
+// in a string of zeroes. (Similar to how it is done in the FlexFEC case.)
+size_t UlpfecHeaderWriter::MinPacketMaskSize(const uint8_t* packet_mask,
+ size_t packet_mask_size) const {
+ return packet_mask_size;
+}
+
+size_t UlpfecHeaderWriter::FecHeaderSize(size_t packet_mask_size) const {
+ return UlpfecHeaderSize(packet_mask_size);
+}
+
+void UlpfecHeaderWriter::FinalizeFecHeader(
+ uint16_t seq_num_base,
+ const uint8_t* packet_mask,
+ size_t packet_mask_size,
+ ForwardErrorCorrection::Packet* fec_packet) const {
+ // Set E bit to zero.
+ fec_packet->data[0] &= 0x7f;
+ // Set L bit based on packet mask size. (Note that the packet mask
+ // can only take on two discrete values.)
+ bool l_bit = (packet_mask_size == kUlpfecPacketMaskSizeLBitSet);
+ if (l_bit) {
+ fec_packet->data[0] |= 0x40; // Set the L bit.
+ } else {
+ RTC_DCHECK_EQ(packet_mask_size, kUlpfecPacketMaskSizeLBitClear);
+ fec_packet->data[0] &= 0xbf; // Clear the L bit.
+ }
+ // Copy length recovery field from temporary location.
+ memcpy(&fec_packet->data[8], &fec_packet->data[2], 2);
+ // Write sequence number base.
+ ByteWriter<uint16_t>::WriteBigEndian(&fec_packet->data[2], seq_num_base);
+ // Protection length is set to entire packet. (This is not
+ // required in general.)
+ const size_t fec_header_size = FecHeaderSize(packet_mask_size);
+ ByteWriter<uint16_t>::WriteBigEndian(&fec_packet->data[10],
+ fec_packet->length - fec_header_size);
+ // Copy the packet mask.
+ memcpy(&fec_packet->data[12], packet_mask, packet_mask_size);
+}
+
+} // namespace webrtc

Powered by Google App Engine
This is Rietveld 408576698