Using Supplemental Enhancement Information (SEI)

Scenarios

• You can use SEI to pass timestamps, calculate end-to-end network latency, or synchronize data with your other services.
• You can use SEI to pass bit control information. You can pass 8 bytes (64 bits) of data. Each bit or group of bits can represent control information, which you can use to transmit instructions for your services.

Sample code

The following code examples show how to use SEI to pass a timestamp.

• iOS and Mac
  • Sender:

    NSTimeInterval now = [[NSDate dateWithTimeIntervalSinceNow:0] timeIntervalSince1970];
    long long lNow = CFSwapInt64BigToHost((long long)(now * 1000));
    NSData * timeData = [NSData dataWithBytes:&lNow length:sizeof(lNow)];
    [self.engine sendMediaExtensionMsg:timeData repeatCount:5];

  • Receiver:

    - (void)onMediaExtensionMsgReceived:(NSString *)uid message:(NSData *)data {
        long long receivedLongLongValue = 0;
        [data getBytes:&receivedLongLongValue length:8];
        long long sentTime= CFSwapInt64BigToHost(receivedLongLongValue);
        NSTimeInterval now = [[NSDate dateWithTimeIntervalSinceNow:0] timeIntervalSince1970];
        long long nowTime= (long long)(now * 1000);
      NSLog(@"%@", [NSString stringWithFormat:@"uid: %@, now: %lld, sent: %lld, difference: %lld", uid, nowTime, sentTime, (nowTime-sentTime)];)}

• Android
  • Sender:

    long lNow =System.currentTimeMillis();
    byte b[] = new byte[8];
    ByteBuffer buf = ByteBuffer.wrap(b);
    buf.putLong(l);
    buf.flip();
    mAliRtcEngine.sendMediaExtensionMsg(buf.array(), 5);

  • Receiver:

    public void onMediaExtensionMsgReceived(String uid, byte[] message) {
      super.onMediaExtensionMsgReceived(uid, message);
      ByteBuffer buffer = ByteBuffer.allocate(8);
      buffer.put(message, 0, message.length);
      buffer.flip();
      long sentTime =buffer.getLong();
    }

• Windows
  • Sender:

    char* long2charArr(long long num)
    {
      char* arr = new char[8];
      int x = 56;
      for (int i = 7; i >= 0; i--)
      {
        long long temp = num << x;
        arr[i] = temp >> 56;
        x -= 8;
      }
      return arr;
    }
    
    SYSTEMTIME tmSys;
    GetLocalTime(&tmSys);
    CTime ctmNow(tmSys);
    long long lNow = __int64(ctmNow.GetTime()) * 1000 + tmSys.wMilliseconds;
    char* cNow = long2charArr(lNow);
    mpEngine->sendMediaExtensionMsg((unsigned char*)cNow, 8, 5);
    delete cNow;

  • Receiver:

    long long charArr2long(char* p)
    {
      long long value = 0;
      value = (((long long)p[0] << 56 & 0xFF00000000000000L) |
      ((long long)p[1] << 48 & 0xFF000000000000L) |
      ((long long)p[2] << 40 & 0xFF0000000000L) |
      ((long long)p[3] << 32 & 0xFF00000000L) |
      ((long long)p[4] << 24 & 0xFF000000L) |
      ((long long)p[5] << 16 & 0xFF0000L) |
      ((long long)p[6] << 8 & 0xFF00L) |
      ((long long)p[7] & 0xFFL));
      return value;
    }
    
    void CTutorialDlg::onMediaExtensionMsgReceived(const AliRtc::String &uid, unsigned char* message, int size)
    {
      long long sentTime = charArr2long((char*)message);
    }

Notes