Lyric Synchronization

// In pure audio mode, the main instance (vocal instance) 
// needs to enable black frame padding to carry SEI messages.
NSDictionary *jsonDic = @{
                            @"api": @"enableBlackStream",
                            @"params": 
                                 @{
                                    @"enable": @(1)
                                  }
                          };
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:jsonDic options:NSJSONWritingPrettyPrinted error:nil];
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
[trtcCloud callExperimentalAPI:jsonString];

TXAudioMusicProgressBlock progressBlock = ^(NSInteger progressMs, NSInteger durationMs) {
    // current ntp time
    NSInteger ntpTime = [TXLiveBase getNetworkTimestamp];
    // Notify the song progress, users will scroll the lyrics here.
    NSDictionary *progressMsg = @{
            @"bgmProgressTime":@(progressMs),
            @"ntpTime":@(ntpTime),
            @"musicId": @(musicId),
            @"duration": @(durationMs),
    };
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:progressMsg options:NSJSONWritingPrettyPrinted error:nil];
    NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
    [trtcCloud sendSEIMsg:[jsonString dataUsingEncoding:NSUTF8StringEncoding] repeatCount:1];
};

// local lyrics synchronization
TXAudioMusicProgressBlock progressBlock = ^(NSInteger progressMs, NSInteger durationMs) {
    ...
    // TODO Update the logic of the lyrics control.
    // Determine whether it is necessary to seek the lyrics control 
    // based on the latest progress and the error of the local lyrics progress.
    ...
};

// remote lyrics synchronization.
- (void)onRecvSEIMsg:(NSString *)userId message:(NSData *)message {
    NSError *err = nil;
    NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:message options:NSJSONReadingMutableContainers error:&err];
    if (err || ![dic isKindOfClass:[NSDictionary class]]) {
        // Parsing error.
        return;
    }
    NSInteger bgmProgressTime = [[dic objectForKey:@"bgmProgressTime"] integerValue];
    NSInteger ntpTime = [[dic objectForKey:@"ntpTime"] integerValue];
    int32_t musicId = [[dic objectForKey:@"musicId"] intValue];
    NSInteger duration = [[dic objectForKey:@"duration"] integerValue];
    ...
    // TODO Update the logic of the lyrics control.
    // Determine whether it is necessary to seek the lyrics control 
    // based on the received latest progress and the error of the local lyrics progress.
    ...
}