Trying to save ustream, sometimes the resulting file is empty

[BoD]

Hi!

I have followed the instructions on this page:
http://www.tech-juice.org/2012/05/20...annels-in-vlc/
to find the rtmp address of some ustream channels, and save a few seconds in a file.

Sometimes it works with no problem.
But sometimes, it seems I receive no data, and the resulting file is empty.

Here is an example that works:

$ rtmpdump -v -r "rtmp://ustreamlivefs.fplive.net/ustream1live-live/stream_live_1_1_13027422" -W "http://www.ustream.tv/flash/viewer.swf" --live -o ~/tmp/test.flv --stop 4
RTMPDump v2.4
(c) 2010 Andrej Stepanchuk, Howard Chu, The Flvstreamer Team; license: GPL
ERROR: RTMP_HashSWF: couldn't contact swfurl http://www.ustream.tv/flash/viewer.swf (HTTP error 302)
Connecting ...
WARNING: HandShake: client signature does not match!
INFO: Connected...
Starting Live Stream
For duration: 4.000 sec
INFO: Metadata:
INFO:   author                
INFO:   copyright             
INFO:   description           
INFO:   keywords              
INFO:   rating                
INFO:   title                 
INFO:   presetname            Custom
INFO:   creationdate          Mon Jan 28 14:22:36 2013
INFO:   videodevice           XSplitBroadcaster
INFO:   framerate             30.00
INFO:   width                 1280.00
INFO:   height                720.00
INFO:   videocodecid          avc1
INFO:   avclevel              31.00
INFO:   avcprofile            100.00
INFO:   videodatarate         390.62
INFO:   videokeyframe_frequency0.10
INFO:   audiodevice           VHAudioCustom
INFO:   audiosamplerate       44100.00
INFO:   audiochannels         1.00
INFO:   audioinputvolume      100.00
INFO:   audiocodecid          mp4a
INFO:   audiodatarate         93.75
INFO:   bufferSize            1200k
INFO:   maxBitrate            1200k
INFO:   xsplitBroadcasterVersion1.3.0.85
INFO:   xsplitCoreVersion     1.2.1301.1501 Version 1.2
INFO:   xsplitGameSourceVersion1.1.1.26
INFO:   xsplitMediaLibVersion 2.0.0.195
1061.349 kB / 2.95 sec
Download complete

Here is an example that does NOT work:

$ rtmpdump -v -r "rtmp://ustreamlivefs.fplive.net/ustream1live-live/stream_live_1_1_2298576" -W "http://www.ustream.tv/flash/viewer.swf" --live -o ~/tmp/test.flv --stop 4
RTMPDump v2.4
(c) 2010 Andrej Stepanchuk, Howard Chu, The Flvstreamer Team; license: GPL
ERROR: RTMP_HashSWF: couldn't contact swfurl http://www.ustream.tv/flash/viewer.swf (HTTP error 302)
Connecting ...
WARNING: HandShake: client signature does not match!
INFO: Connected...
Starting Live Stream
For duration: 4.000 sec
0.000 kB / 0.00 sec
Download complete

As you can see it downloaded 0 bytes.

Any idea what could be the problem?

Thanks a lot!