iOS AppRTCMobile: Fix SDP video codec reordering for multiple H264 profiles

webrtc/examples/objc/AppRTCMobile/ARDSDPUtils.m

 /*
  *  Copyright 2015 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.
  */
 
 #import "ARDSDPUtils.h"
 
 #import "WebRTC/RTCLogging.h"
 #import "WebRTC/RTCSessionDescription.h"
 
 @implementation ARDSDPUtils
 
 + (RTCSessionDescription *)
     descriptionForDescription:(RTCSessionDescription *)description
           preferredVideoCodec:(NSString *)codec {
   NSString *sdpString = description.sdp;
   NSString *lineSeparator = @"\n";
   NSString *mLineSeparator = @" ";
   // Copied from PeerConnectionClient.java.
   // TODO(tkchin): Move this to a shared C++ file.
   NSMutableArray *lines =
       [NSMutableArray arrayWithArray:
           [sdpString componentsSeparatedByString:lineSeparator]];
+  // Find the line starting with "m=video".
   NSInteger mLineIndex = -1;
-  NSString *codecRtpMap = nil;
+  for (NSInteger i = 0; i < lines.count; ++i) {
+    if ([lines[i] hasPrefix:@"m=video"]) {
+      mLineIndex = i;
+      break;
+    }
+  }
+  if (mLineIndex == -1) {
+    RTCLog(@"No m=video line, so can't prefer %@", codec);
+    return description;
+  }
+  // An array with all payload types with name |codec|. The payload types are
+  // integers in the range 96-127, but they are stored as strings here.
+  NSMutableArray *codecPayloadTypes = [[NSMutableArray alloc] init];
   // a=rtpmap:<payload type> <encoding name>/<clock rate>
   // [/<encoding parameters>]
   NSString *pattern =
       [NSString stringWithFormat:@"^a=rtpmap:(\\d+) %@(/\\d+)+[\r]?$", codec];
   NSRegularExpression *regex =
       [NSRegularExpression regularExpressionWithPattern:pattern
                                                 options:0
                                                   error:nil];
-  for (NSInteger i = 0; (i < lines.count) && (mLineIndex == -1 || !codecRtpMap);
-       ++i) {
-    NSString *line = lines[i];
-    if ([line hasPrefix:@"m=video"]) {
-      mLineIndex = i;
-      continue;
-    }
+  for (NSString *line in lines) {
     NSTextCheckingResult *codecMatches =
         [regex firstMatchInString:line
                           options:0
                             range:NSMakeRange(0, line.length)];
     if (codecMatches) {
-      codecRtpMap =
-          [line substringWithRange:[codecMatches rangeAtIndex:1]];
-      continue;
+      [codecPayloadTypes
+          addObject:[line substringWithRange:[codecMatches rangeAtIndex:1]]];
     }
   }
-  if (mLineIndex == -1) {
-    RTCLog(@"No m=video line, so can't prefer %@", codec);
-    return description;
-  }
-  if (!codecRtpMap) {
-    RTCLog(@"No rtpmap for %@", codec);
+  if ([codecPayloadTypes count] == 0) {
+    RTCLog(@"No payload types with name %@", codec);
     return description;
   }
   NSArray *origMLineParts =
       [lines[mLineIndex] componentsSeparatedByString:mLineSeparator];
-  if (origMLineParts.count > 3) {
-    NSMutableArray *newMLineParts =
-        [NSMutableArray arrayWithCapacity:origMLineParts.count];
-    NSInteger origPartIndex = 0;
-    // Format is: m=<media> <port> <proto> <fmt> ...
-    [newMLineParts addObject:origMLineParts[origPartIndex++]];
-    [newMLineParts addObject:origMLineParts[origPartIndex++]];
-    [newMLineParts addObject:origMLineParts[origPartIndex++]];
-    [newMLineParts addObject:codecRtpMap];
-    for (; origPartIndex < origMLineParts.count; ++origPartIndex) {
-      if (![codecRtpMap isEqualToString:origMLineParts[origPartIndex]]) {
-        [newMLineParts addObject:origMLineParts[origPartIndex]];
-      }
-    }
-    NSString *newMLine =
-        [newMLineParts componentsJoinedByString:mLineSeparator];
-    [lines replaceObjectAtIndex:mLineIndex
-                     withObject:newMLine];
-  } else {
+  // The format of ML should be: m=<media> <port> <proto> <fmt> ...
+  const int kHeaderLength = 3;
+  if (origMLineParts.count <= kHeaderLength) {
     RTCLogWarning(@"Wrong SDP media description format: %@", lines[mLineIndex]);
+    return description;
   }
+  // Split the line into header and payloadTypes.
+  NSRange headerRange = NSMakeRange(0, kHeaderLength);
+  NSRange payloadRange =
+      NSMakeRange(kHeaderLength, origMLineParts.count - kHeaderLength);
+  NSArray *header = [origMLineParts subarrayWithRange:headerRange];
+  NSMutableArray *payloadTypes = [NSMutableArray
+      arrayWithArray:[origMLineParts subarrayWithRange:payloadRange]];
+  // Reconstruct the line with |codecPayloadTypes| moved to the beginning of the
+  // payload types.
+  NSMutableArray *newMLineParts = [NSMutableArray arrayWithCapacity:origMLineParts.count];
+  [newMLineParts addObjectsFromArray:header];
+  [newMLineParts addObjectsFromArray:codecPayloadTypes];
+  [payloadTypes removeObjectsInArray:codecPayloadTypes];
+  [newMLineParts addObjectsFromArray:payloadTypes];
+
+  NSString *newMLine = [newMLineParts componentsJoinedByString:mLineSeparator];
+  [lines replaceObjectAtIndex:mLineIndex
+                   withObject:newMLine];
+
   NSString *mangledSdpString = [lines componentsJoinedByString:lineSeparator];
   return [[RTCSessionDescription alloc] initWithType:description.type
                                                  sdp:mangledSdpString];
 }
 
 @end