Transmit absolute time

Sebastian Dröge sebastian at
Wed Oct 14 06:02:37 PDT 2015

On Di, 2015-10-13 at 17:18 +0200, Pietro Bonfa' wrote:
> My main goal is to estimate the time difference between various frames
> acquired from many devices.
> This means I would opt for "transfer accurate timestamps as metadata" in
> your list.

So you only need to know the timestamps, not synchronise the media
according to them? If you use RTP/RTSP, you could use an header
extension like the one from RFC6051. But that one is for NTP
timestamps, you could do the same for PTP timestamps.
Alternatively some kind of metadata stream could also be used.

For the NTP header extension, I have some half finished code here that
needs some finishing. Additionally you would need to ensure that on the
sender side, the pipeline is using the PTP clock and the PTP clock is
used as the "NTP" clock for RTP.

> I really look forward to see your presentation. I searched for your
> slides on the gstreamer website but I could not find them. Are they
> available somewhere else?

If your mailbox is big enough, I can send them to you. Or upload them
somewhere otherwise. But I guess they are not too useful without what I
said during the presentation :)

> Finally, I read your post about PTP and I can correctly interface the
> PTP server with gstreamer thanks to your work so...thank you!
> And thanks also for your time.

You're welcome! Let me know if there's something not working well with
these things, and how well the PTP clock works for your use cases :)

Sebastian Dröge, Centricular Ltd ·

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