Add function for getting supported H264 level from max resolution and fps

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 <cstdio>
 #include <cstdlib>
 #include <cstring>
 
+#include "webrtc/base/arraysize.h"
+
 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.
@@ skipping 34 matching lines @@
 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}};
 
+struct LevelConstraint {
+  const int max_macroblocks_per_second;
+  const int max_macroblock_frame_size;
+  const webrtc::H264::Level level;
+};
+
+// This is from ITU-T H.264 (02/2016) Table A-1 – Level limits.
+static constexpr LevelConstraint kLevelConstraints[] = {
+    {1485, 99, webrtc::H264::kLevel1},
+    {1485, 99, webrtc::H264::kLevel1_b},
+    {3000, 396, webrtc::H264::kLevel1_1},
+    {6000, 396, webrtc::H264::kLevel1_2},
+    {11880, 396, webrtc::H264::kLevel1_3},
+    {11880, 396, webrtc::H264::kLevel2},
+    {19800, 792, webrtc::H264::kLevel2_1},
+    {20250, 1620, webrtc::H264::kLevel2_2},
+    {40500, 1620, webrtc::H264::kLevel3},
+    {108000, 3600, webrtc::H264::kLevel3_1},
+    {216000, 5120, webrtc::H264::kLevel3_2},
+    {245760, 8192, webrtc::H264::kLevel4},
+    {245760, 8192, webrtc::H264::kLevel4_1},
+    {522240, 8704, webrtc::H264::kLevel4_2},
+    {589824, 22080, webrtc::H264::kLevel5},
+    {983040, 3684, webrtc::H264::kLevel5_1},
+    {2073600, 3684, webrtc::H264::kLevel5_2},
+};
+
 }  // 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);
@@ skipping 41 matching lines @@
     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>();
 }
 
+rtc::Optional<Level> SupportedLevel(int max_frame_pixel_count, int max_fps) {
+  static const int kPixelsPerMacroblock = 16 * 16;
+
+  for (int i = arraysize(kLevelConstraints) - 1; i >= 0; --i) {
+    const LevelConstraint& level_constraint = kLevelConstraints[i];
+    if (level_constraint.max_macroblock_frame_size * kPixelsPerMacroblock <=
+            max_frame_pixel_count &&
+        level_constraint.max_macroblocks_per_second <=
+            max_fps * level_constraint.max_macroblock_frame_size) {
+      return rtc::Optional<Level>(level_constraint.level);
+    }
+  }
+
+  // No level supported.
+  return rtc::Optional<Level>();
+}
+
 rtc::Optional<std::string> ProfileLevelIdToString(
     const ProfileLevelId& profile_level_id) {
   // Handle special case level == 1b.
   if (profile_level_id.level == kLevel1_b) {
     switch (profile_level_id.profile) {
       case kProfileConstrainedBaseline:
         return rtc::Optional<std::string>("42f00b");
       case kProfileBaseline:
         return rtc::Optional<std::string>("42100b");
       case kProfileMain:
@@ skipping 26 matching lines @@
       return rtc::Optional<std::string>();
   }
 
   char str[7];
   snprintf(str, 7u, "%s%02x", profile_idc_iop_string, profile_level_id.level);
   return rtc::Optional<std::string>(str);
 }
 
 }  // namespace H264
 }  // namespace webrtc