[MPlayer-dev-eng] MPLAYER Support for RTCP extensions anb dynamic playback buffer management

[Mario Montagud Climent]

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.  
(http://personales.gan.upv.es/~fboronat/Research/index_investig_en.html)

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  
appropriated solution.

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  
library.

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,

Mario

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  
2008.

[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.