(OBSOLETE) Increasing audio buffer on Iphone 4S.

webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.m

Index: webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.m
diff --git a/webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.m b/webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.m
index d2d04835499fe9ee990f546ddda01cc787d5cf39..05c0c2259d5028ddd4a54dd9221389ecd73aeb60 100644
--- a/webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.m
+++ b/webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.m
@@ -10,6 +10,8 @@
 
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.h"
 
+#import <sys/utsname.h>
+
 #import "WebRTC/RTCDispatcher.h"
 
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSession.h"
@@ -44,6 +46,11 @@ const double kRTCAudioSessionLowComplexitySampleRate = 16000.0;
 // sequence without bursts of callbacks back to back.
 const double kRTCAudioSessionHighPerformanceIOBufferDuration = 0.01;
 
+// Use a larger buffer size on iphone 4S to allow it running complex tasks
+// e.g., encoding long frames with Opus codec.

[henrika_webrtc, 2016/06/17 07:37:37]

nit, I would say large frames

[minyue-webrtc, 2016/06/23 11:35:07]

Done.

+NSString* const kIphone4sDeviceTyp = @"iPhone4,1";
+const double kRTCAudioSessionHighPerformanceIOBufferDurationIphone4s = 0.02;
+
 // Use a larger buffer size on devices with only one core (e.g. iPhone 4).
 // It will result in a lower CPU consumption at the cost of a larger latency.
 // The size of 60ms is based on instrumentation that shows a significant
@@ -80,11 +87,22 @@ static RTCAudioSessionConfiguration *gWebRTCConfiguration = nil;
     // to ensure that the I/O unit does not have to do sample rate conversion.
     // Set the preferred audio I/O buffer duration, in seconds.
     NSUInteger processorCount = [NSProcessInfo processInfo].processorCount;
+
+    struct utsname systemInfo;

[henrika_webrtc, 2016/06/17 07:37:37]

Please compare with existing methods in
https://cs.chromium.org/chromium/src/third_party/webrtc/modules/utility/sourc....
They are designed for mixed C++/ObjC but should be useful here as well.

[minyue-webrtc, 2016/06/23 11:35:07]

Done.

+    uname(&systemInfo);
+    NSString *device_type = [NSString stringWithCString:systemInfo.machine
+                                               encoding:NSUTF8StringEncoding];
+
     // Use best sample rate and buffer duration if the CPU has more than one
     // core.
     if (processorCount > 1) {
       _sampleRate = kRTCAudioSessionHighPerformanceSampleRate;
-      _ioBufferDuration = kRTCAudioSessionHighPerformanceIOBufferDuration;
+      if ([device_type isEqualToString:kIphone4sDeviceTyp]) {
+        _ioBufferDuration =
+            kRTCAudioSessionHighPerformanceIOBufferDurationIphone4s;
+      } else {
+        _ioBufferDuration = kRTCAudioSessionHighPerformanceIOBufferDuration;
+      }
     } else {
       _sampleRate = kRTCAudioSessionLowComplexitySampleRate;
       _ioBufferDuration = kRTCAudioSessionLowComplexityIOBufferDuration;