[Live-devel] Expose RTP Timestamp as public in RTPSource

[Ross Finlayson]

> On May 13, 2020, at 2:05 AM, Lionel Koenig <lionel.koenig at codemill.se> wrote:
> 
> Hi,
> In order to achieve very precise digital audio converter clock synchronisation between server and client in a project I am currently working on, I need to access the exact RTP timestamp of the last packet from my MediaSink so I can precisely estimate the clock differences. Using presentation  timestamps is subject to clock adjustment

Sorry, but you seem to be misunderstanding what the presentation time (as seen by the RTP/RTCP receiver does).  It (once RTCP synchronization has started) *already* gives you an exact representation of the RTP timestamp, and thus the LIVE555 libraries do not (and never will) expose the RTP timestamps to the receiver; that would give you no more information (and only lead to potential confusion).  The LIVE555 library automatically converts RTP timestamps to presentation times (and vice versa for servers).  Applications that use the LIVE555 libraries never need to concern themselves with RTP timestamps.

If you haven’t done so already, see
	http://live555.com/liveMedia/faq.html#separate-rtp-streams
and
	http://live555.com/liveMedia/faq.html#rtcp-synchronization-issue

Note that the RTP timestamps (and thus, presentation times) are in based on the server’s (i.e., sender’s) clock. If there is clock drift between the sender and receivers’ clocks, then you might find that, over time, the presentation times shift compared to the receiver’s clock.  A RTP receiver application (e.g., a media player) is supposed to take account of this, and - if necessary - compensate by occasionally dropping or duplicating samples.

Alternatively, if both server and client are under your control, then you might find it worthwhile to synchronize their system clocks - e.g., using NTP.


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/