Add functionality for parsing H264 profile-level-id

webrtc/common_video/h264/profile_level_id.cc

+/*
+ *  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/common_video/h264/profile_level_id.h"
+
+#include <cstdlib>
+#include <cstring>
+
+namespace {
+
+// For level_idc=11 and profile_idc=0x42, 0x4D, or 0x58, the constraint set3
+// flag specifies if level 1b or level 1.1 is used.
+const uint8_t kConstraintSet3Flag = 0x10;
+
+// Convert a string of 8 characters into a byte where the positions containing
+// character c will have their bit set. For example, c = 'x', str = "x1xx0000"
+// will return 0b10110000. constexpr is used so that the pattern table in
+// kProfilePatterns is statically initialized.
+constexpr uint8_t ByteMaskString(char c, const char (&str)[9]) {
+  return (str[0] == c) << 7
+      | (str[1] == c) << 6
+      | (str[2] == c) << 5
+      | (str[3] == c) << 4
+      | (str[4] == c) << 3
+      | (str[5] == c) << 2
+      | (str[6] == c) << 1
+      | (str[7] == c) << 0;
+}
+
+// Class for matching bit patterns such as "x1xx0000" where 'x' is allowed to be
+// either 0 or 1.
+class BitPattern {
+ public:
+  constexpr BitPattern(const char (&str)[9])
+      : mask_(~ByteMaskString('x', str)),
+        masked_value_(ByteMaskString('1', str)) {}
+
+  bool IsMatch(uint8_t value) const { return masked_value_ == (value & mask_); }
+
+ private:
+  const uint8_t mask_;
+  const uint8_t masked_value_;
+};
+
+// Table for converting between profile_idc/profile_iop to H264::Profile.
+struct ProfilePattern {
+  const uint8_t profile_idc;
+  const BitPattern profile_iop;
+  const webrtc::H264::Profile profile;
+};
+
+// This is from https://tools.ietf.org/html/rfc6184#section-8.1.
+constexpr ProfilePattern kProfilePatterns[] = {
+    {0x42, BitPattern("x1xx0000"), webrtc::H264::kProfileConstrainedBaseline},
+    {0x4D, BitPattern("1xxx0000"), webrtc::H264::kProfileConstrainedBaseline},
+    {0x58, BitPattern("11xx0000"), webrtc::H264::kProfileConstrainedBaseline},
+    {0x42, BitPattern("x0xx0000"), webrtc::H264::kProfileBaseline},
+    {0x58, BitPattern("10xx0000"), webrtc::H264::kProfileBaseline},
+    {0x4D, BitPattern("0x0x0000"), webrtc::H264::kProfileMain},
+    {0x64, BitPattern("00000000"), webrtc::H264::kProfileHigh},
+    {0x64, BitPattern("00001100"), webrtc::H264::kProfileConstrainedHigh}};
+
+}  // anonymous namespace
+
+namespace webrtc {
+namespace H264 {
+
+rtc::Optional<ProfileLevelId> ParseProfileLevelId(const char* str) {
+  // The string should consist of 3 bytes in hexadecimal format.
+  if (strlen(str) != 6u)
+    return rtc::Optional<ProfileLevelId>();
+  const uint32_t profile_level_id_numeric = strtol(str, nullptr, 16);
+  if (profile_level_id_numeric == 0)
+    return rtc::Optional<ProfileLevelId>();
+
+  // Separate into three bytes.
+  const uint8_t level_idc =
+      static_cast<uint8_t>(profile_level_id_numeric & 0xFF);
+  const uint8_t profile_iop =
+      static_cast<uint8_t>((profile_level_id_numeric >> 8) & 0xFF);
+  const uint8_t profile_idc =
+      static_cast<uint8_t>((profile_level_id_numeric >> 16) & 0xFF);
+
+  // Parse level based on level_idc and constraint set 3 flag.
+  Level level;
+  switch (level_idc) {
+    case kLevel1_1:
+      level = (profile_iop & kConstraintSet3Flag) != 0 ? kLevel1_b : kLevel1_1;
+      break;
+    case kLevel1:
+    case kLevel1_2:
+    case kLevel1_3:
+    case kLevel2:
+    case kLevel2_1:
+    case kLevel2_2:
+    case kLevel3:
+    case kLevel3_1:
+    case kLevel3_2:
+    case kLevel4:
+    case kLevel4_1:
+    case kLevel4_2:
+    case kLevel5:
+    case kLevel5_1:
+    case kLevel5_2:
+      level = static_cast<Level>(level_idc);
+      break;
+    default:
+      // Unrecognized level_idc.
+      return rtc::Optional<ProfileLevelId>();
+  }
+
+  // Parse profile_idc/profile_iop into a Profile enum.
+  for (const ProfilePattern& pattern : kProfilePatterns) {
+    if (profile_idc == pattern.profile_idc &&
+        pattern.profile_iop.IsMatch(profile_iop)) {
+      return rtc::Optional<ProfileLevelId>({pattern.profile, level});
+    }
+  }
+
+  // Unrecognized profile_idc/profile_iop combination.
+  return rtc::Optional<ProfileLevelId>();
+}
+
+}  // namespace H264
+}  // namespace webrtc