[MPlayer-dev-eng] MPLAYER Support for RTCP extensions anb dynamic playback buffer management
Mario Montagud Climent
mamontor at upvnet.upv.es
Mon Dec 19 10:00:22 CET 2011
Dear MPLAYER developers,
This is my first message to this mailing list.
My name is Mario Montagud. I am a PhD student at Politechnic
University of Valencia (UPV) in Spain. I am working under Prof.
Fernando Boronat supervision.
I?m a newbie in mplayer. So, I would like to ask you some information
about the ?udp_sync? module and the mplayer capabilities.
My PhD work is about Multimedia Communications and Synchronization
Techniques. Concretely, our research group is designing an
Inter-Destination Multimedia Synchronization (IDMS) proposal that aims
to synchronize the playout of media streams across separated clients.
For that purpose, we take advantage of the feedback and extension
capabilities of RTP/RTCP protocols.
You can find more information about the preliminary version of our
IDMS approach in the reference [Bor08], in which it was implemented by
using VIC (for video) and RAT (for audio) mbone tools, and tested in a
real scenario (our University WAN).
In the initial stages of my PhD, I have implemented this IDMS approach
in a network simulator (NS-2), and I?ve added some enhancements to
that solution (see [Bor11]).
Currently, an evolved version of our IDMS proposal is under
standardization status within the IETF (see ref [Bra11]). We are
collaborating in its specification/design in conjunction with some
Dutch researchers from TNO (Delft).
On the one hand, a new RTCP report block (RTCP XR for IDMS block) has
been specified to inform the source (or a sync manager) about receipt
and playout times for specific RTP media packets (for that purpose all
the participants must share a common available clock source, e.g. NTP,
GPS, or other solutions ?). On the other hand a new RTCP packet type
(RTCP IDMS packet) has been defined to send playout setting
instructions to the sync clients (if an out of sync situation is
detected by the sync manager).
My next objective is to implement and test that IDMS proposal in a
real media player/framework. So, I?m searching for the most
I have found some related work, such as the ?udp_sync? module in
mplayer, and the ?netsync? module in VLC media player.
I think the ?udp_sync? module in mplayer is used to synchronize
different local video files (not a network stream) by using the
master's position in the file: the master just sends out a broadcast
UDP datagram with its position in the file anytime it plays a frame,
and the slaves play that frame. It does nothing to adjust for
variable network latency.
However, our goal is to synchronize an RTP network stream across
multiple dispersed clients. For that purpose, we use the global time
instant (64-bit wall clock time, e.g. NTP) at which a specific RTP
packet has been received (or played out) by each sync client.
For that purpose, we need to implement the new RTCP packet types and
block reports defined in [Bra11]. I think it should be done in live555
I think the most difficult task will be the management of the playout
processes in each media client to get in sync (e.g. to report on
presentation time for a specific RTP packet ?e.g. the last one
encapsulating a video frame-, and to dynamically manage the necessary
playback adjustments, playout speed variation? Skips/pauses?).
Do you think mplayer is a good choice for implementing our
RTP/RTCP-based IDMS solution?
Can I access to the playback buffer to know about presentation times
of a specific video frame and the current playback buffer occupancy?
Your comments will be much appreciated.
Thank you very much in advance.
Regards from Spain,
REFERENCES: (If you are interested but you don?t have access to them,
please tell me)
[Bor08] F. Boronat, J.C. Guerri, and J. Lloret, ?An RTP/RTCP based
approach for multimedia group and inter-stream synchronization?,
Multimedia Tools and Applications Journal, Vol. 40 (2), 285-319, June
[Bor11] F. Boronat, M. Montagud, and V. Vidal, ?Smooth Control of
Adaptive Media Playout to Acquire IDMS in Cluster-based Applications?,
IEEE LCN 2011, Bonn, October 2011.
[Bra11] R. V. Brandenburg, H. Stokking, M.O. V. Deventer, Boronat, F.
M. Montagud, K. Gross, ?RTCP for Inter-Destination Media
Synchronization?, IETF Internet Draft, October 2011.
More information about the MPlayer-dev-eng