Parsing of encoded duration for unencrypted opus streams.

media/formats/webm/opus_packet_builder.cc

Index: media/formats/webm/opus_packet_builder.cc
diff --git a/media/formats/webm/opus_packet_builder.cc b/media/formats/webm/opus_packet_builder.cc
new file mode 100644
index 0000000000000000000000000000000000000000..21aff160630baba37449f52b1b74241b773d4133
--- /dev/null
+++ b/media/formats/webm/opus_packet_builder.cc
@@ -0,0 +1,81 @@
+#include "media/formats/webm/opus_packet_builder.h"
+#include "media/formats/webm/webm_cluster_parser.h"
+
+namespace media {
+
+// From Opus RFC. See http://goo.gl/2RmoxA
+enum OpusConstants {
+  kNumPossibleOpusConfigs = 32,
+  kMinOpusPacketFrameCount = 1,
+  kMaxOpusPacketFrameCount = 48
+};
+
+OpusPacketInfo::OpusPacketInfo() {
+}
+OpusPacketInfo::~OpusPacketInfo() {
+}
+
+scoped_ptr<OpusPacketInfo> BuildOpusPacket(int config,

[wolenetz, 2015/02/03 22:47:01]

ISTM that this could be a constructor. Also, the data member could lazily be
constructed in a .data() accessor. OpusPacketInfo could then be renamed to
OpusPacket. This seems a little more aligned with existing test data
abstractions like ClusterBuilder. WDYT?

[chcunningham, 2015/02/05 02:48:20]

Done.

+                                           int frame_count,
+                                           bool is_VBR) {
+  scoped_ptr<OpusPacketInfo> packet_info(new OpusPacketInfo());
+  packet_info->toc_config = config;
+  packet_info->frame_count = frame_count;
+  packet_info->duration_ms =
+      frame_count * (WebMClusterParser::kOpusFrameDurationsMu[config] /
+                     static_cast<float>(1000));
+
+  int frame_count_code;
+  uint8 frame_count_byte;

[wolenetz, 2015/02/03 22:47:01]

_t

[chcunningham, 2015/02/05 02:48:21]

Done.

+
+  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 opus_toc_byte = (config << 3) | frame_count_code;
+  packet_info->data.push_back(opus_toc_byte);
+
+  // For code 3 packets, the number of frames is signalled in the "frame
+  // count byte".
+  if (frame_count_code == 3) {
+    packet_info->data.push_back(frame_count_byte);
+  }
+
+  // Simulating encoded frame data.
+  packet_info->data.push_back(static_cast<uint8>(0));
+
+  return packet_info.Pass();
+}
+
+// Builds an exhaustive collection of Opus packet configurations.

[wolenetz, 2015/02/03 22:47:01]

nit: move method comment to .h

[chcunningham, 2015/02/05 02:48:21]

Done.

+std::vector<scoped_ptr<OpusPacketInfo>> BuildAllOpusPackets() {
+  std::vector<scoped_ptr<OpusPacketInfo>> 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(
+          BuildOpusPacket(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(
+            BuildOpusPacket(opus_config_num, frame_count, is_VBR));
+      }
+    }
+  }
+
+  return opus_packets;
+}
+
+}  // namespace media