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cnetwork-programmingtimestamprtpntp

how media in rtp is synchronized?

I am trying to understand how the timestamp in rtp along with some time synchronization protocol like ntp, can synchronize the media streams. Based on my understanding I have drawn this. Please correct me if I'm wrong.

Here clock in these devices are synchronized, and rtp packet is created with timestamp 10. But due to network transmission delay the packet reaches at 11, but the timestamp is still 10. How this case is handled in rtp for proper synchronization or is it the application that is taking care of this situation?

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Solution

  • When handling an incoming (UDP) RTP stream, received RTP packets will be buffered before they are processed. This is to allow for jitter and such. This buffering period is typically between 50 and 300 milliseconds, depending on the used network topology.

    If the buffering time is adjustable at runtime, you could use this buffering period to synchronize the two streams by ear. When two streams are out of sync adjust the buffering time (delay) of one of the streams until they appear in-sync.

    If you don't want, or can't, adjust the buffering period by ear you should use RTCP (RFC 3550) to synchronize the two streams. You can't just use the timestamp values in the RTP packets.

    I think this website with FAQs on RTP can be helpful.