iOS WebView内联播放视频无声音

_webView.allowsInlineMediaPlayback = YES;

//Enable Audio
NSError *error;
[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:&error];
if (error) {
    NSLog(@"Error in setting category = %@", error);
    //handle error here.
}
[[AVAudioSession sharedInstance] setActive:YES error:&error];
if (error) {
    NSLog(@"Error in activating session = %@", error);
    //handle error here.
}