[Live-devel] QuickTime Broadcaster, Axis Network Cameras and Live555

[Richard Kunert]

I've noticed some interesting / aggravating behavior using live555 as  
included in VLC to record rtsp audio streams from QuickTime  
Broadcaster and video from a pair of Axis network cameras. I'm hoping  
someone here can shed some light on it.

The problem is that mpeg-4 rtsp audio and streams saved to  
QuickTime .mov files are set to 75% of their correct duration (file  
size is normal). This is very repeatable. After a (long) period of  
troubleshooting I found the RTCP decoder in Wireshark and looked at  
the packets Broadcaster is sending. The NTP timestamps are in local  
time, not UTC as defined in RFC 3550.

The obvious workaround for this was to set the time zone of the  
machine running QuickTime Broadcaster to GMT. That fixes the problem  
completely. With no other changes I can turn the data truncation on  
and off just by changing the time zone on that machine. Putting it in  
GMT results in properly recorded files, any other time zone and I'm  
back at 75% duration.

A few more data points:

I have identical results with mpeg-4 rtsp video streams from my Axis  
cameras. 75% duration. Unfortunately they don't seem to be capable of  
producing a correct RTCP timestamp at all. I'm really curious about  
this 75% number as it seems to be unrelated to any parameters of the  
streams.

These are actually part of a system that's been in production for  
about a year. I've been running my streams through QuickTime Streaming  
Server and recording the resulting stream. QTSS somehow "fixes" the  
stream so that the duration is correct (or at least it used to, Mac OS  
X updates last December appear to have broken it). This is in spite of  
the fact that it doesn't appear to modify the RTCP timestamps that  
Broadcaster puts out. My preliminary hypothesis is that the RTCP  
timestamps, if present and correct, are used to fix some other problem  
in the chain.

The setup:
Quicktime Broadcaster streaming MPEG-4 audio over RTSP (44.1KHz AAC,  
64Kbps).
Two Axis network cameras streaming MPEG-4 video over RTSP.
Lectures are streamed live using QuickTime Streaming Server.
Streams are captured to disk using three scripted instances of VLC  
pointed at the streaming server.
All software is the latest version as of this date.
All streams from the cameras and Broadcaster are multicast, but I get  
the same results with unicast streams.
No firewall issues.
Nothing interesting gets logged from VLC with it set to maximum  
verboseness.

Any illumination / speculation would be MUCH appreciated. If this  
sounds like some other part of VLC is likely to be closer to the issue  
I'll take my question over there.

--
Richard Kunert