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

webrtc/examples/objc/AppRTCMobile/ARDSDPUtils.m

Index: webrtc/examples/objc/AppRTCMobile/ARDSDPUtils.m
diff --git a/webrtc/examples/objc/AppRTCMobile/ARDSDPUtils.m b/webrtc/examples/objc/AppRTCMobile/ARDSDPUtils.m
index 3a8a578dc68fccf47cab303d315866749a494893..9552936924519e16f38f5ff814e3853b9d6d7c08 100644
--- a/webrtc/examples/objc/AppRTCMobile/ARDSDPUtils.m
+++ b/webrtc/examples/objc/AppRTCMobile/ARDSDPUtils.m
@@ -27,7 +27,9 @@
       [NSMutableArray arrayWithArray:
           [sdpString componentsSeparatedByString:lineSeparator]];
   NSInteger mLineIndex = -1;
-  NSString *codecRtpMap = nil;
+  // 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 =
@@ -36,8 +38,7 @@
       [NSRegularExpression regularExpressionWithPattern:pattern
                                                 options:0
                                                   error:nil];
-  for (NSInteger i = 0; (i < lines.count) && (mLineIndex == -1 || !codecRtpMap);
-       ++i) {
+  for (NSInteger i = 0; i < lines.count; ++i) {
     NSString *line = lines[i];
     if ([line hasPrefix:@"m=video"]) {
       mLineIndex = i;
@@ -48,17 +49,16 @@
                           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) {

[daniela-webrtc, 2016/11/21 16:23:00]

can we extract the check for the "m=video" even before the loop?
For instance, perhaps some nicer form of the following nested if*
if (![sdpString hasPrefix:@"m=video"]) {
  if (![sdpString containsString:@"\nm=video"]) {
  //handle the use case when no m=video line has been found
  }
}

*this if nest is purely to demonstrate the logic I'm suggesting :)

[magjed_webrtc, 2016/11/22 14:40:24]

Done, I extracted finding the "m=video" line out from this for-loop.

     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 =
@@ -71,9 +71,9 @@
     [newMLineParts addObject:origMLineParts[origPartIndex++]];
     [newMLineParts addObject:origMLineParts[origPartIndex++]];
     [newMLineParts addObject:origMLineParts[origPartIndex++]];
-    [newMLineParts addObject:codecRtpMap];
+    [newMLineParts addObjectsFromArray:codecPayloadTypes];

[daniela-webrtc, 2016/11/21 16:23:00]

Perhaps we can extend the usage of methods of NSMutableArray further and perhaps
get rid of the origPartIndex and the second for loop.
Something like *: 
 if (origMLineParts.count > 3) {
    NSMutableArray *newMLineParts =	 
         [NSMutableArray arrayWithArray:origMLineParts];
    [newMLineParts removeObjectsInArray:codecPayloadTypes];	
    [newMLineParts insertObjects:codecPayloadTypes atIndexes:[...]];
}
I don't know the usage of insertObjects:atIndexes: by heart, but this link
should provide enough info on the usage
https://developer.apple.com/reference/foundation/nsmutablearray/1416482-inser...

* this is not working code, purely to demonstrate the logic :)

[magjed_webrtc, 2016/11/22 14:40:24]

Done, I tried my best to make it cleaner.

     for (; origPartIndex < origMLineParts.count; ++origPartIndex) {
-      if (![codecRtpMap isEqualToString:origMLineParts[origPartIndex]]) {
+      if (![codecPayloadTypes containsObject:origMLineParts[origPartIndex]]) {
         [newMLineParts addObject:origMLineParts[origPartIndex]];
       }
     }