解决ios下使用uiwebview载入网页时，插放网页中视频或者音频无声音解决办法

<pre name="code" class="objc">- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.

AVAudioSession *audioSession = [AVAudioSession sharedInstance];
BOOL ok;
NSError *setCategoryError = nil;
ok = [audioSession setCategory:AVAudioSessionCategoryPlayback        error:&setCategoryError];
if (!ok) {
NSLog(@"%s setCategoryError=%@", __PRETTY_FUNCTION__, setCategoryError);
}
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