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
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