Parsing of encoded duration for unencrypted opus streams.

media/formats/webm/opus_packet_builder.cc

+// Copyright (c) 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/logging.h"
+#include "media/formats/webm/opus_packet_builder.h"
+#include "media/formats/webm/webm_cluster_parser.h"
+
+namespace media {
+
+// From Opus RFC. See https://tools.ietf.org/html/rfc6716#page-14
+enum OpusConstants {
+  kNumPossibleOpusConfigs = 32,
+  kMinOpusPacketFrameCount = 1,
+  kMaxOpusPacketFrameCount = 48
+};
+
+OpusPacket::OpusPacket(uint8_t config, uint8_t frame_count, bool is_VBR) {
+  DCHECK_GE(config, 0);
+  DCHECK_LT(config, kNumPossibleOpusConfigs);
+  DCHECK_GE(frame_count, kMinOpusPacketFrameCount);
+  DCHECK_LE(frame_count, kMaxOpusPacketFrameCount);
+
+  duration_ms_ = frame_count *
+                 WebMClusterParser::kOpusFrameDurationsMu[config] /
+                 static_cast<float>(1000);
+
+  uint8_t frame_count_code;
+  uint8_t frame_count_byte;
+
+  if (frame_count == 1) {
+    frame_count_code = 0;
+  } else if (frame_count == 2) {
+    frame_count_code = is_VBR ? 2 : 1;
+  } else {
+    frame_count_code = 3;
+    frame_count_byte = (is_VBR ? 1 << 7 : 0) | frame_count;
+  }
+
+  // All opus packets must have TOC byte.
+  uint8_t opus_toc_byte = (config << 3) | frame_count_code;
+  data_.push_back(opus_toc_byte);
+
+  // For code 3 packets, the number of frames is signaled in the "frame
+  // count byte".
+  if (frame_count_code == 3) {
+    data_.push_back(frame_count_byte);
+  }
+
+  // Packet will only conform to layout specification for the TOC byte
+  // and optional frame count bytes appended above. This last byte
+  // is purely dummy padding where frame size data or encoded data might
+  // otherwise start.
+  data_.push_back(static_cast<uint8_t>(0));
+}
+
+OpusPacket::~OpusPacket() {
+}
+
+const uint8_t* OpusPacket::data() const {
+  return &(data_[0]);
+}
+
+int OpusPacket::size() const {
+  return data_.size();
+}
+
+double OpusPacket::duration_ms() const {
+  return duration_ms_;
+}
+
+ScopedVector<OpusPacket> BuildAllOpusPackets() {
+  ScopedVector<OpusPacket> opus_packets;
+
+  for (int frame_count = kMinOpusPacketFrameCount;
+       frame_count <= kMaxOpusPacketFrameCount; frame_count++) {
+    for (int opus_config_num = 0; opus_config_num < kNumPossibleOpusConfigs;
+         opus_config_num++) {
+      bool is_VBR = false;
+      opus_packets.push_back(
+          new OpusPacket(opus_config_num, frame_count, is_VBR));
+
+      if (frame_count >= 2) {
+        // Add another packet with VBR flag toggled. For frame counts >= 2,
+        // VBR triggers changes to packet framing.
+        is_VBR = true;
+        opus_packets.push_back(
+            new OpusPacket(opus_config_num, frame_count, is_VBR));
+      }
+    }
+  }
+
+  return opus_packets.Pass();
+}
+
+}  // namespace media