Implement WiFi Display elementary stream packetizer.

extensions/renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.cc

Index: extensions/renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.cc
diff --git a/extensions/renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.cc b/extensions/renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a1f686a66d1593452064cd0317f495cda988aad3
--- /dev/null
+++ b/extensions/renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.cc
@@ -0,0 +1,176 @@
+// Copyright 2016 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 "extensions/renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.h"
+
+#include <cstring>
+
+#include "base/logging.h"
+
+namespace extensions {
+namespace {
+
+// Packetized Elementary Stream (PES)
+namespace pes {

[asargent_no_longer_on_chrome, 2016/03/16 22:47:57]

Is any of the code here used outside of this .cc file? If not, we typically use
unnamed namespaces instead of named ones for that. See:

http://dev.chromium.org/developers/coding-style#TOC-Unnamed-namespaces
https://google.github.io/styleguide/cppguide.html#Namespaces

(I'm not sure there's a hard and fast rule *against* using named namespaces for
code that's local to a .cc file, but it's certainly unusual in the extensions
code, so probably best to match the local style)

[e_hakkinen, 2016/03/17 15:29:26]

No, it is not used outside of this .cc file (and cannot be used as it is within
an anonymous namespace).
It is an anonymous namespace (extensions::(anonymous namespace)::pes).
IMHO, it is useful as it documents that what is inside it comes from the PES
specification.

WDYT?

It is of course less relevant here than in WiFiDisplayTransportStreamPacketizer
(https://crrev.com/1797953002/patch/40001/50005) where there are pieces from the
PES (Program Specific Information) specification, from TS (MPEG Transport
Stream) specification and from the WiDi (WiFi Display) specification.

[asargent_no_longer_on_chrome, 2016/03/17 18:22:59]

Ok, that makes sense. You might just consider making the comment slightly more
descriptive, e.g. something like:

// Code related to the Packetized Elementary Stream (PES) specification
namespace pes {
  ...
}  // namespace pes


but I'll leave that up to you. 

+
+const size_t kOptionalHeaderBaseSize = 3u;
+const size_t kPacketHeaderBaseSize = 6u;
+const size_t kTimeStampSize = 5u;
+const size_t kPacketHeaderMaxSize =
+    kPacketHeaderBaseSize + kOptionalHeaderBaseSize + 2u * kTimeStampSize;
+
+const size_t kUnitDataAlignment = 4u;
+
+size_t FillInTimeStamp(uint8_t* dst,
+                       uint8_t pts_dts_indicator,
+                       const base::TimeTicks& ts) {
+  // Convert to the number of 90 kHz ticks since some epoch.
+  // Always round up so that the number of ticks is never smaller than
+  // the number of program clock reference base ticks (which is not rounded
+  // because program clock reference is encoded with higher precision).
+  const uint64_t us =
+      static_cast<uint64_t>((ts - base::TimeTicks()).InMicroseconds());
+  const uint64_t n = (us * 90u + 999u) / 1000u;
+
+  // Expand PTS DTS indicator and a 33 bit time stamp to 40 bits:
+  //  * 4 PTS DTS indicator bits, 3 time stamp bits, 1 on bit
+  //  * 15 time stamp bits, 1 on bit
+  //  * 15 time stamp bits, 1 on bit
+  size_t i = 0u;
+  dst[i++] = (pts_dts_indicator << 4) | (((n >> 30) & 0x7u) << 1) | (0x1u << 0);
+  dst[i++] = (n >> 22) & 0xFFu;
+  dst[i++] = (((n >> 15) & 0x7Fu) << 1) | (0x1u << 0);
+  dst[i++] = (n >> 7) & 0xFFu;
+  dst[i++] = (((n >> 0) & 0x7Fu) << 1) | (0x1u << 0);
+  DCHECK_EQ(i, kTimeStampSize);
+  return i;
+}
+
+size_t FillInOptionalHeader(uint8_t* dst,
+                            const base::TimeTicks& pts,
+                            const base::TimeTicks& dts,
+                            size_t unit_header_size) {
+  size_t i = 0u;
+  dst[i++] = (0x2u << 6) |  // Marker bits (0b10)
+             (0x0u << 4) |  // Scrambling control (0b00 for not)
+             (0x0u << 3) |  // Priority
+             (0x0u << 2) |  // Data alignment indicator (0b0 for not)
+             (0x0u << 1) |  // Copyright (0b0 for not)
+             (0x0u << 0);   // Original (0b0 for copy)
+  const uint8_t pts_dts_indicator =
+      !pts.is_null() ? (!dts.is_null() ? 0x3u : 0x2u) : 0x0u;
+  dst[i++] = (pts_dts_indicator << 6) |  // PTS DTS indicator
+             (0x0u << 5) |               // ESCR flag
+             (0x0u << 4) |               // ES rate flag
+             (0x0u << 3) |               // DSM trick mode flag
+             (0x0u << 2) |               // Additional copy info flag
+             (0x0u << 1) |               // CRC flag
+             (0x0u << 0);                // Extension flag
+  const size_t header_length_index = i++;
+  const size_t optional_header_base_end_index = i;
+  DCHECK_EQ(i, kOptionalHeaderBaseSize);
+
+  // Optional fields:
+  // PTS and DTS.
+  if (!pts.is_null()) {
+    i += FillInTimeStamp(&dst[i], pts_dts_indicator, pts);
+    if (!dts.is_null())
+      i += FillInTimeStamp(&dst[i], 0x1u, dts);
+  }
+
+  // Stuffing bytes (for unit data alignment).
+  const size_t remainder =
+      (kPacketHeaderBaseSize + i + unit_header_size) % kUnitDataAlignment;
+  if (remainder) {
+    const size_t n = kUnitDataAlignment - remainder;
+    std::memset(&dst[i], 0xFF, n);
+    i += n;
+  }
+
+  dst[header_length_index] = i - optional_header_base_end_index;
+  return i;
+}
+
+size_t FillInPacketHeader(uint8_t* dst,
+                          uint8_t stream_id,
+                          const base::TimeTicks& pts,
+                          const base::TimeTicks& dts,
+                          size_t unit_header_size,
+                          size_t unit_size) {
+  // Reserve space for packet header base.
+  size_t i = kPacketHeaderBaseSize;
+  const size_t header_base_end_index = i;
+
+  // Fill in optional header.
+  i += FillInOptionalHeader(&dst[i], pts, dts, unit_header_size);
+
+  // Compute packet length.
+  size_t packet_length =
+      (i - header_base_end_index) + unit_header_size + unit_size;
+  if (packet_length >> 16) {
+    // The packet length is too large to be represented. That should only
+    // happen for video frames for which the packet length is not mandatory
+    // but may be set to 0, too.
+    DCHECK_GE(static_cast<unsigned>(stream_id),
+              WiFiDisplayElementaryStreamPacketizer::kFirstVideoStreamId);
+    DCHECK_LE(static_cast<unsigned>(stream_id),
+              WiFiDisplayElementaryStreamPacketizer::kLastVideoStreamId);
+    packet_length = 0u;
+  }
+
+  // Fill in packet header base.
+  size_t j = 0u;
+  dst[j++] = 0x00u;  // Packet start code prefix (0x000001).

[asargent_no_longer_on_chrome, 2016/03/16 22:47:57]

nit: this comment is sort of confusing - it's not immediately clear to me why
you have "(0x000001)" in the comment when the value being set is 0x00u

[e_hakkinen, 2016/03/17 15:29:26]

Added " in three bytes".

[asargent_no_longer_on_chrome, 2016/03/17 18:22:59]

ah, thanks, that makes it much more clear

+  dst[j++] = 0x00u;
+  dst[j++] = 0x01u;
+  dst[j++] = stream_id;
+  dst[j++] = packet_length >> 8;
+  dst[j++] = packet_length & 0xFFu;
+  DCHECK_EQ(j, kPacketHeaderBaseSize);
+
+  return i;
+}
+
+}  // namespace pes
+
+}  // namespace
+
+WiFiDisplayElementaryStreamPacket::WiFiDisplayElementaryStreamPacket(
+    const HeaderBuffer& header_data,
+    size_t header_size,
+    const uint8_t* unit_header_data,
+    size_t unit_header_size,
+    const uint8_t* unit_data,
+    size_t unit_size)
+    : header_(header_buffer_, header_size),
+      unit_header_(unit_header_data, unit_header_size),
+      unit_(unit_data, unit_size) {
+  // Copy the actual header data bytes from the |header_data| argument to
+  // the |header_buffer_| member buffer used in the member initialization list.
+  std::memcpy(header_buffer_, header_data, header_size);
+}
+
+WiFiDisplayElementaryStreamPacket
+WiFiDisplayElementaryStreamPacketizer::EncodeElementaryStreamUnit(
+    uint8_t stream_id,
+    const uint8_t* unit_header_data,
+    size_t unit_header_size,
+    const uint8_t* unit_data,
+    size_t unit_size,
+    const base::TimeTicks& pts,
+    const base::TimeTicks& dts) {
+  if (!unit_header_data) {
+    DCHECK_EQ(0u, unit_header_size);
+    unit_header_data = unit_data;
+  }
+
+  uint8_t header_data[pes::kPacketHeaderMaxSize];
+  size_t header_size = pes::FillInPacketHeader(header_data, stream_id, pts, dts,
+                                               unit_header_size, unit_size);
+  return WiFiDisplayElementaryStreamPacket(header_data, header_size,
+                                           unit_header_data, unit_header_size,
+                                           unit_data, unit_size);
+}
+
+}  // namespace extensions