Add to-string function for H264 profile level id

webrtc/common_video/h264/profile_level_id.cc

Index: webrtc/common_video/h264/profile_level_id.cc
diff --git a/webrtc/common_video/h264/profile_level_id.cc b/webrtc/common_video/h264/profile_level_id.cc
index 9f9aef9f61d147f72111b6ee3d6f5c79395e00d6..4b5be2d239efffc59767b10dd102c51c590e8b56 100644
--- a/webrtc/common_video/h264/profile_level_id.cc
+++ b/webrtc/common_video/h264/profile_level_id.cc
@@ -10,6 +10,7 @@
 
 #include "webrtc/common_video/h264/profile_level_id.h"
 
+#include <cstdio>
 #include <cstdlib>
 #include <cstring>
 
@@ -128,5 +129,48 @@ rtc::Optional<ProfileLevelId> ParseProfileLevelId(const char* str) {
   return rtc::Optional<ProfileLevelId>();
 }
 
+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 "42f00b";
+      case kProfileBaseline:
+        return "42100b";
+      case kProfileMain:
+        return "4D100b";
+      // Level 1b is not allowed for other profiles.
+      default:
+        return std::string();

[kthelgason, 2016/11/03 09:39:05]

Maybe we should return an rtc::Optional<std::string> here, so the callee doesn't
have to remember to check for an empty string.

[magjed_webrtc, 2016/11/03 12:31:16]

You are probably right. It's clearer than returning an empty string and the type
system will enforce checking against it.

+    }
+  }
+
+  const char* profile_idc_iop_string;
+  switch (profile_level_id.profile) {
+    case kProfileConstrainedBaseline:
+      profile_idc_iop_string = "42e0";
+      break;
+    case kProfileBaseline:
+      profile_idc_iop_string = "4200";
+      break;
+    case kProfileMain:
+      profile_idc_iop_string = "4D00";
+      break;
+    case kProfileConstrainedHigh:
+      profile_idc_iop_string = "640c";
+      break;
+    case kProfileHigh:
+      profile_idc_iop_string = "6400";
+      break;
+    // Unrecognized profile.
+    default:
+      return std::string();

[kthelgason, 2016/11/03 09:39:05]

perhaps replace this with a RTC_NOTREACHED() if we expect this to never happen.

[magjed_webrtc, 2016/11/03 12:31:16]

If we handle some case, then we should not CHECK/NOT_REACHED also. This is from
the style guide:
"... A consequence of this is that you should not handle DCHECK() failures, even
if failure would result in a crash. Attempting to handle a DCHECK() failure is a
statement that the DCHECK() can fail, which contradicts the point of writing the
DCHECK()."

+  }
+
+  char str[7];
+  snprintf(str, 7u, "%s%02x", profile_idc_iop_string, profile_level_id.level);
+  return str;
+}
+
 }  // namespace H264
 }  // namespace webrtc